Meaningful family games or activities for gatherings?

Our extended family lives in the same city and we're always getting together (brother/sisters-in-laws, their kids). So basically our generation and our kids. Probably 13-15 of us.

We meet maybe once or twice a month, but whenever we meet, kids just go do kids things, dads go over here, moms go over there. One of the dads invariably falls asleep, one or two of the kids kind of mull about not quite fitting in here or there.

I was wondering if any of you had any ideas for something that can be done together that might help build memories or at least structure some time so that there's meaningful interaction and we can get to know each other better instead of defaulting to whatever is least effort.

The only constraint is that is has to be that it's an in-home, indoor activity suitable for teens/pre-teens.