Is there a higher likelihood of being placed in a particular building if your group is a certain size? By that I mean, do they save certain areas or rooms for the larger families?

Agree with others. We requested adjoining rooms, but got rooms next to each other instead. No biggie. It's based on availability. There are some unofficial WDW websites that give you hints that might improve your chances with room requests. Google WDW room requests and do some research. Hope this helps

I don't believe so. I went in a group of 15 people last week. They put us in the Alligator Bayou (about a 7 minute walk from the lobby) in 3 rooms. They were not adjoining. 2 were next to each other and the other was downstairs. We didn't request a specific room, but we did ask them to keep us together. I assume this was the best they could do. I do recall reading you can try to request a certain building, so I would advise giving them a call to see if they'll let you do that.

I don't believe they have family rooms, just preferred rooms or view rooms. For large families you may need to book an extra room.

You could ask and they'll try to accommodate you.

Agree with all other comments, based on availability.

We just booked 3 rooms, they were all beside each other.

No, all the rooms are the same, just the beds differ. You should be placed based on availability, unless a specific request can be accommodated, but this would just be 2 rooms next to each other at best.