Bed envy???

[emu81]

Hi
My DD (4y) and DS (18m) have been sharing a bedroom since December, all went without any issues until the last two weeks. Now DS does not want to nap or go to sleep (he has always been a pretty good sleeper) and cries, screams and shouts angrily from 7.30pm until between 8-9pm, he also wakes up between 4-6am. He had been sleeping 7.30pm - 7am. DD starts off in our room and sleeps through nightime/early morning wake ups. He does nap after his crying/screaming symphony but now only for 1hr before I need to get my DD from nursery.
He does not have any teeth coming through at the moment (one did recently come through). He has been becoming an increasingly fussy eater (over last couple of months) and has been biting, pinching DD and pulling her hair more.
He settles very well in DD's bed (gets in and pulls the covers up, doesn't want to get out)
Could the aversion to sleep be due to DS being envious of DD's bed as he is still in a cot? is it worth taking the side off his cot to give him a 'big bed' or could it be just that this is the horrible two's starting?
Any advice would be gratefully received!!