I'm in the same boat. Ds3 doesn't sleep pretty much at all while the big boys are up! He's four months now. Luckily my big boys still nap 3.5 and 2 years... So he'll sleep on me in the hug a bub or not sleep at all... I just try to go with the flow and not stress about it. Seems to work for us.
We all have colds at the moment so ds1 and 2 are particularly crabby and ds3 won't sleep full stop unless there's a booby in his mouth! Even through the night! I'm sick to so struggling!
Apologies for the rant! Goodluck with working something out