We ended up putting the mattresses on the floor and sleeping as a family. Not ideal. But it worked. We still often all end up in one room (we have 2 double mattresses on the floor) to sleep. Even DD who is 5 1/2 will still come in sometimes.
I used to feed DS1 and pat DD but she never tantrumed or screamed she just couldn't settle herself to sleep and cried if I left her. When DS2 came along, I did the same with DS1. I laid in bed DS2 on the boob and DS1 and DD was on her own bed. As long as I was in the room she was happy, but I had to be with DS1 in the bed or he wouldn't settle. Now they're bigger I can just sit with DS2 on his bed, and sit in the room with the bigger kids until they fall asleep.