Scummymummy - this is a very difficult one! I know how very difficult it is to spend enough one-to-one time with each of my 3 children, although it has got slightly easier now the eldest is at school full-time and the middle one is at playschool 5 mornings a week. I imagine that your boys, as twins, are very close, do they mind being apart from each other, or would this be the first hurdle you face?
Speaking from my own experience, my eldest 2 love playing on the computer, and have some great fun children's educational games (so are learning at the same time). I know your boys are still quite young, but do you think that they could manage one of the easier games (eg. Tweenies or Bob the Buider) where thy just have to control the mouse? If so, you could put one on the computer and do cooking/painting/drawing etc. with the other, and then swap over.
Another idea is to let one play at one of their friend's houses (which they love to do) and you do something with the other one (go to the park/play in the garden) and then swap over another day.
If you and dp both have your weekends off together, perhaps for just 1 hour a day you could each do something with one son, and then swap over the next day. That way it wouldn't really interfere with your dp catching up with both boys. It would also be nice for both of you to see each of their own personalities and characters in their own right. All of my 3 children are so different, it's hard to think that they are brothers and sister sometimes!
I hope that my ideas don't seem too idealistic to you, and might be of some use. Don't worry yourself too much about this, Scummymummy, you and dp both sound like good, caring parents and I'm sure that your children are lovely, happy little boys.
As for the eye contact, I'm sure my eldest ds didn't look at me when I was talking to him at your sons' age, and at age 5, he still doesn't!! (neither does dh at age 32 - do you think it's a boy/man thing?) Actually, on a more serious note, are you sure that he can hear you properly? My ds has glue ear (we're waiting to hear what will be done about it) so sometimes he just can't hear me when I'm talking to him.