My 16 month old has been the same with his 2 month old brother. I have noticed that he was doing it for attention so I have given more time just for the eldest,. I have also let the eldest go to his brother and since allowing him to do so he ends up kissing or cuddling him. Try not to tell him off as any attention is good attention in their eyes. Also lots of praise when they are playing independently, helping or just being kind. It will get better but you do have to remember that it's a huge change for them as it is for us. It will get easier and you are doing a fantastic job
Unpopular opinion so pls don’t come at me but try training them. My sister does this with her kids and it is very effective. When your toddler kicks or smacks etc then flick them once on their hand. It will immediately grab their attention and stop what they are doing, they will probably cry but once they have calmed down then you tell them why you have flicked them and then hug them, love them etc. please note though that this is training them, not punishing them. Do not flick more than once in one go and obviously not too hard! It’s just meant to give them a fright, not hurt them. It quickly teaches them that what they are doing is wrong. Distraction doesn’t work. It teaches them nothing.
Sounds like you need to wear your baby to keep him safe from your toddler. Also, teach him that he has to be gentle with his brother.
He’s so loving towards him always has been, he gives him cuddles and kisses off his own back, helps me feed him and play with him but he just has intrusive impulsive thoughts, I manage to stop him 90% of the time. His dad works but I don’t and I live far away from any help. He’s going to nursery in December for 2 half days a week, I spend plenty of time with him when baby sleeps, loads of toys and books, outside time every day. He’s not speaking yet and I’m assuming it’s about attention. I try be inclusive as much as I can.
My sister kid is 3 and does the same to my 3 months old daughter they just jealous as dont get as much attention as before. Whenever the baby is in bed try to give him 1:1 play together etc so he sees you haven't replaced him. Try to involve him like hey you pass me the nappy pass me the tissue. Show your sibling your toy etc. Come gently touch the baby etc. But until he settles around the baby try either to keep them in separate rooms or carry the baby
Does your 2 yo go to nursery? Where is dad when this is happening? Do you have any family around you to come over etc?