Hi there
My sister has 9 month old twins and she has managed to get them having a good 2 hour sleep at lunchtime since about 6 months. I have been trying to pick her brains as my 7.5month old daughter rarely sleeps for longer than 45 mins - 1 hour at lunchtime. She said that she just left them (for up to 20 mins ) if they cried, and left them completely if they were awake but happy. However, I have tried this with my dd and it definitely hasn't worked - she seems to have had enough sleep and just wants to get up and play. I usually get her up if she's having a scream, but I know that with twins you are probably more desperate for a bit of consistent time to yourself !!
Oh, and my sister's twins nap in different rooms during the day, but do sleep in their room together overnight.
I would love some advice as to how to extend this lunchtime nap too, as I only let dd have about half an hour kip in the morning so she should be pretty tired for a nice long sleep by lunchtime !
good luck