Note that, according to Clue 7, there can also be no “P” in any last name in the family. So Tom’s family must take their letters from MNO**RST, and now the only four letters that can satisfy Clue 6 can be MORT.

Not that MPRTPN is a very common last name, but still…

Thanks for posting this, ArtVark!

There are only two last names here since wives and kids take
the husbands last name. Tim, Tom, Otis, and Rose all have
one last name. Paul, Hildy, Sean, Josie, and Lisa have the
other last name.

Tim’s sister in law is Rose whose maiden name was the other
family’s last name. Since it is a cryptogram of her current
last name, both last name must contain the same number of
letters.

Sean’s brother in law is Tom. Tom’s last name is twice
as long as his first name, and spans the exact same range
of letters as his first name. Since no last name has a
Q, his last name must span the letters MNOPRST.

Paul’s grandson Otis also has the same last name as Tom.
In order for the first four letters of his name to be
in the range MNORPRST to be in alphabetical order without
being consecutive letters, these letters have to be MORT.

So one family’s name is MORT__. Sean, Lisa’s father is
in the other side of the family and their last name must
be in the pattern __N_A_ (third and fifth letters and
the last two letters in Sean’s first name). Hildy’s
fourth letter in her first name is also the fourth letter
in her last name, so, that last name must be __NDA_.
Lisa has the same letter starting both her first name
and last name, so the name has to be L_NDA_. Since
Paul shares a common second letter with his last name,
the name is LANDA_. Finally, one of the two last names
has a U. Since the letters in the other last name are
in the range MNOPRST, the only place for a U is to make
this last name LANDAU.

Since LANDAU is a cryptogram of MORT__, the other name
must be MORTO_. Now Otis has two uncles, one whose
last name ends with the third letter of the last name
of his other uncle. Therefore, the last letter in this
name has to be N, making it MORTON.

Since Otis Morton was the first person in the restaurant,
Morton should be the name that they are looking for.

Tom arrived after his sister-in-law, who never married. This
is Hildy. Hildy’s sister-in-law did not make it to the dinner.
This is Josie. So there are at least three siblings: Hildy,
her brother married to Josie, and her sister married to Tom.

Now Otis is related by blood to everyone at the dinner. In order
for Otis to be related to Tom, he has to be somewhere in the
lineage of Tom’s portion of the tree. In order to be related to
Hildy, he has to be in a portion of that tree. This could only
happen if Otis were the son of Tom and his wife (Hildy’s sister).
(He could be a grandson or even more generations removed, but
given the number of limited number of people in this family
and the fact that he is Paul’s grandson, he has to be their son.).

Therefore Otis is Tom’s son. If Otis had an unmarried sibling,
that person would also be a blood relative of everyone there.
Since Otis was the only one who was related by blood to
everyone, Otis has no siblings. If Otis were married, his
wife would not be a blood relative. Therefore Otis is not
married. Finally, if Otis had a married sibling, Otis would
not be blood related to his sibling’s spouse. Therefore, Otis
has no siblings and is unmarried.

Now Paul must be either Tom’s father, or Tom’s wife’s father,
because he is Otis’s grandfather. If he were Tom’s father,
then Rose would be Tom’s sister. The only remaining female
not placed would be Lisa who would have to be Tom’s wife. This
would make one of Sean and Tim Lisa’s father, and the other
Lisa’s brother who is married to Josie. If this were the
case, then all the family members will have been placed with
no brothers. Since there was a pair of brothers, Paul could not
be Tom’s father. Therefore he is the father of Tom’s wife, Hildy,
and Josie’s husband.

If Lisa were Tom’s wife, Paul would have had to have come in
between the two brothers Otis and Tim. But we have already
established that Otis has no siblings. Therefore, Lisa can
not be Tom’s wife. By process of elimination, his wife must
be Rose.

Now Josie’s husband can only be Sean or Tim. If he were Tim,
in order for Tim to have a sister-in-law, Tim must have a
brother who would have to be Sean. Sean would have to be
married to Lisa (the only remaining female). If this were
the case, Otis would have no blood relation with Lisa.
Therefore Josie’s husband must be Sean.

Lisa’s father came in between two brothers. He can’t be Paul
(between Otis with no siblings and Tim) and he can’t be Tim
(between Paul and Sean who are father and son). Therefore,
Lisa’s father must be Sean, and the brothers must be Tim and
Tom.

So there are three generations in this family. Paul is in
the first generation, and his children are Rose, Hildy, and Sean.
Rose is married to Tom and their child is Otis. Sean is married
to Josie and their child is Lisa. Tim is Tom’s brother.

Otis, Josie, and Lisa are the key names to start with.
Anyone who was not the first or last person in has
to have two other people with whom they do not share
any letters in their last names. Lisa can only be
before or after Tom, and Otis and Josie can only be
before or after Paul (this can all be derived from
applying Rule 11 to every possible name). One of
these three people has to be first, one has to be
last, and one has to be the one who did not make it
to the dinner.

The missing person was Hildy’s sister-in-law and
therefore female, so Otis was there and came in either
first or eighth (last). Paul would then have to
be second or seventh. If Josie were at the dinner,
then she would be either third or sixth which is
impossible (no other person could be next to Josie
without violating Rule 11). Therefore, Josie had
to be the person who missed the dinner.

Otis and Lisa have to be the first and last ones in.
Paul and Tom have to be the second and seventh in.

If Otis were the last one in, Paul would be seventh,
Lisa first, and Tom second. Paul came in after his
grandson, which now can be either Tim or Sean. Since
Paul and Sean both have the letter A, it can only be
Tim. In this case, third, fourth and fifth have to
be Hildy, Sean, and Rose. Sean and Rose could not
have come in next to each other (they both have S and
E in their names), so Hildy would have to be in the
middle. If Rose were third, she would be after Tom
with whom her name shares an O. If Rose were fifth
then she would be after Hildy. However, she had to
have come in immediately after her father instead of
Hildy. Therefore this situation is impossible, and
Otis could not have been the last person in. The
only possible place Otis could have come in would
be first.

Therefore, Otis came in first, Paul second, Tom
seventh, and Lisa eighth.

Now of the remaining four people, Sean and Rose can
not be next to each other. Also, Tim and Hildy can
not be next to each other. Tim and Rose also cannot
be sixth (next to Tom). So the only possible orders
for these four is Tim, Rose, Hildy, Sean or Rose, Tim,
Sean, Hildy. Since Tom came in immediately after his
sister-in-law, Hildy has to be in front of Tom instead
of Sean. Therefore the order that the people came in
is:

Otis, Paul, Rose, Tim, Sean, Hildy, Tom, Lisa

Once they’ve had a fair crack at it, I’ll post a complete solution here.

Seems like such a waste to give away the answer before any legitimate problem solvers (sorry Brian) look at it. I would urge you to post this over at the forum, and not even link to here. You should really give someone else the opportunity to work through it and not quarter-ass it like me.

But you must have figured out at least some of it to get to the point where you could guess. How far were you able to get? I’m happy to fill in the rest.

You may want to redirect some of those Ken Jennings forum people over here.