I haven't flown with two under two but I have flown with a baby and a just-over 2 year old, and again alone transatlantically with a baby, a just over 2 and a 4 year old.

It can be done. You learn to change them standing up (as soon as they can stand with support). You use the handicapped lavs for more room. Some aircraft have bigger lavs like the ones aft on 747's (not all though).

When I went to the restroom, I made sure whomever wasn't going was strapped into their car seat (sleeping usually) and then told someone where I was (F/A or fellow passenger so if the child woke up, which happened once). Awake children went with me.

I only flew twice with a lap child. Once, I didn't make the reservation (and forgot to discuss this with who did) and another time it was on Air France, who wont accept my car seat so I wasn't paying for a seat if I couldn't use my car seat. Both were small babies.

I will admit that as a Flight Attendant, I saw some pretty uncomfortable flights with large toddlers on laps. A girlfriend in RL just did it and said it was dire. We're talking only one lap child so be warned...