We did 3 generations last trip and will be doing the same this trip.
As far as expenses, depends on the financial situation and you need to be prepared to pay for your own families expenses, but be grateful if someon with deeper pockets wants to pay for some things. Communication is important.
Last year we shared a room with my parents, I paid the deposit but my parents then paid for the rest. I paid for my AP, they paid for their tickets and DS's. We flew down on their FF miles.
This year we are going with my sister and family, and my mother. My sister's husband is a big spender, wants to eat at Signature resturants and will order $50 or appitizers each meal, expensive drinks, etc. I'll try to ask for my bill seperately, I'm already really worried about how we will handle that. I'm on a tight budget. Also I don't expect my mother to pay for meals for the whole group, but perhaps my sis and BIL expect she will be footing part of the bill? Mom and I are sharing a room and splitting the cost of that.
As far as touring, my kids are 11 yrs apart. I had a carefully planned minute by minute itinerary where we split up occasionally to accomodate both kids, grandma and grandpa took DD to Dumbo while DS and I rode Space, etc. But mostly, we all stuck together. There were only 5 of us then, the grandparents, myself and my two kids.