I am not sure if this would help since my DD1 is 5 and not 3 but here is what I do. I lay down with DD2 (who is 2) for an hour for her nap. While I do that I have DD1 play quietly in her room and I set an alarm for her. When the alarm goes off she can come and wake me up and we can have some one on one time. I am not sure if your 3 yo is old enough for this but it works for us. Maybe just 20 minutes or a half an hour, long enough to get the youngest down to sleep in a dark room? I know not everyone likes videos but it may help occupy him too during that time and give you a little more peace and quiet. Sometimes a mama's got to do what a mama's got to do.
I only have one child but she was similar with sleep and activity as a baby and now as well. No advice but sympathy.
Have you considered posting this question over in the 'parenting the gifted child' forum? Sleep comes up fairly often there and you might receive some helpful advice.
Unschooling Mother to S, my 6yo "Moon Farmer"
DH(9/04) DS(12/08) and DD(5/11)
No advice, but lots and lots of sympathy, here. I take care of my 6mo nephew a few days a week and getting him down for a nap when my 15mo son is ready to play? Almost impossible. I've resorted to calling it "snack time" and sitting my son in his high chair with a little snack, some water, and turning on Blue's Clues . Otherwise he screams and bangs on the door and no nap for the little one.
DD 12/07 DS 9/10