I am just adding to that. I do not know your real situation so I am just extrapolating. It could be that his siblings are taking a good share of parental attention that was once fully his. Especially his mother's.
If so, you will need to patiently work with him to show you are fair to all kids. Once the mother is free enough to spend time with him, this behaviour will subside. She will currently be having her hands full with the little ones and you might have to pitch in.
With time and patience he will be back to his calm self. Next to your 3 and 1 year old, he might seem older but remember that he is still just a kid and not too emotionally different from a 3 year old.
When, the going gets difficult, remember this too shall pass and some time in the future, you will use this experience to help out another harried parent!
Outdoor free play can release some of the kid's pent-up energy and that certainly helps
Ensure the kid is getting enough sleep too.