Just catching up on your PTR from before you posted you were officially booked and I just wanted to say





YIPPIE!!!!
I loved seeing your family pictures at Christmas. I imagine Christmas is never boring with your family - my kind of day!
Now for your plans:
OK i told ya i would come back.
So Day 2 is the kids birthday. I really wanted to do the dessert party on their birthday. So i believe Epcot might be our arrival day we can wave at the castle on the way to our room (if we can see it) or we might be heading over to another resort? not going to think about that right now..
OK this may sound better..
Day 1 arrival day head on over to Epcot? or whatever park has EMH at night. whichever we need to go and say HI to Mickey tell him we have arrived!!! Ohana dinner. get a good night sleep for the BIG day..
Day 2 BIRTHDAY!!! yep their actual birthday. SO dessert party on this day.. Doesn't necessarily mean it has to be a MK day.. all depends on what time Wishes is going to happen! again can't do too much until the times are out.
Day 3 sleep in get as much sleep as possible because another late night for MNSSHP which i would love to do BOG for dinner Party usually starts at 7? but allow people in at 4??
Day 4 late start day want to be very low key.. Maybe HS for Scifi dinner OR our total down day and head over to DTD raglan road Hope for a day that has EMH at night
Day 5 AK Tusker house Breakfast
Day 6 depends on crowd calendar HS or Epcot
Day 7 depends on Crowd calendar Epcot or HS maybe hit Mk to say goodbye to the castle?
Day 8 D-day Resort day with Ohana breakfast.
This plan sounds good to me. I love that you will be doing the dessert party for the muchkins's actual birthday.

Staying in the park and seeing the fireworks is so much better then the pirate cruise (not that I've been to either). That castle show is really enjoyable (in my personal opinion). And then not having to rush off to a park the next morning will be a nice treat.
A few questions/comments -
If you plan on going to Epcot on arrival day I would try to make a reservation for dinner there so you don't have to rush back to the Poly for dinner. Unless Ohana is the priority then your quick visit to Epcot would be fun, especially since you are on the monorail.
Your MNSSHP day - you can usually tell which days they will have the party based on the previous years calendar. I know in late Sept / early Oct they have the party on more then two nights. We have always gone in Oct/Nov/Dec so I always need to plan around the parties and if you look back you can see the pattern or if you haven't already, check for someone's predictions on the disboards. We have never actually gone to one of the parties (my kids are not nightowls by any stretch and I am just too cheap to pay for the extra tickets since they probably won't get to enjoy the party). We do usually hit MK on a party day and have found the crowds to be very light up until about 4:30 when the party crowds start to enter.
Lots of folks try to get early reservations in the park for the party so they can hit the ground running at 7 pm. I know if you want to do things like meet the dwarfs or Jack and Sally you have to be in line WAY before 7 pm.
A while back Nini posted that she felt she had better/faster service with a smaller party size then when her entire group (7 I think) ate at the same time. As a party of 6 (automatic gratuity) we have experienced the same thing and it seems to take us at least 90 minutes to 2 hours to have a meal at an ADR. The servers just don't seem to be in a rush to get our drinks, get our dessert orders or even bring our check. So you might want to factor that in when you are going to be eating with Jen's family. The only exception we had to that was at Kona cafe on your last trip where we had GREAT service and a GREAT meal.
Your day after the party at HS sounds like a good choice. With FP+ you can schedule a later ride on Toy Story Mania and enjoy that park even with a later start. Plus that park is smaller and you can probably do it in a shorter day.
I would totally plan on going to MK another day (6 or 7) depending on the crowd calendar, only because I love MK and we always spend 3 days there concentrating on a different section of the park and doing our favorites on each day . Like I said, MK on the party days is usually low crowds and that might be a good night to try and get BOG. I think we had a 6 or 6:30 ADR there on a party night and we were literally the last people in there. We had the castle to ourselves and were escorted to the front of the park (since we were not staying for the party). We scheduled our FP+ for Enchanted Tales with Belle right before our dinner reservation so we saw Belle and then Beast. We have also done MK on a party night and then gone to Chef Mickey for dinner. I know the theory is to avoid the MK on Saturdays as there are usually lots of locals plus the regular crowds.
Just wanted to make sure that your trip is not Sept 5 or 6 since they are having the Night of Joy nights there on those days. I think they are at the MK and it closes early.
Sorry for the long ramble. I'm so excited that your trip is getting down to about 7 months away. I too am impressed that you have kept the secret so long and I love that the kids are saving money for a trip.