15 month old DS pinching,biting, pulling hair Help

[Ray81]

I have 3 DCs, DD1 is 11 DD2 is 3 and DS1 is 15 months.

I am currently having a nightmare with DS hitting, pinching, biting and pulling The hair of DD2, I don't know what to do I have tried ignoring it, moving him away and giving the attention to DD2 but this seems to make him worse, I have tried the controversial doing it back but tbh this isn't effective when you can't bring yourself to actually hurt them when doing it back ifkwim.

Has anyone else ever had this problem ? And have any advise to give please. It's getting to the point where I can't even step out of the room for 5 seconds without him doing something and I am pulling my hair out.

Any help would be greatly appreciated.

This is probably quite an obvious question - is DD2 doing anything to him? When you are not looking? If not, sounds like the terrible twos. If it is a recent behaviour and you are sure DD2 is not involved, just keep rewarding her with attention/small treat. The first time you leave them alone successfully be ready to reward him for not doing anything to his sister. HTH and

No I am pretty sure DD2 isn't doing anything to him, an example is we were sat on the sofa this morning and he just reached over and pinched her, literally out of no where. When I have left them together I will stop At the door and look through the gap and again he will just suddenly pull hair, pinch etc. I could understand it if she was doing something to him but that just isn't the case.
Don't get me wrong she's not an angel and she will snatch toys etc but she isn't violent ifkwim

Think I may have to just keep ignoring and hope it passes.