R.B.
we had/have this with our two little ones now.
What worked for us was when holding the baby letting him sit on our lap also. Let him gently poke and pat and play with her. After a week he wasn't jealous or interested in her at all. The only thing he went back to was needing a bottle when she got one. So against all advice we let him have a couple of ounces of water in it and he was happy. Now that she can move around and is mobile he will jump into a jealousy mode and we let him on us and play with him (even if she is crying) and after 5 mins of full attention he is good and will even go down to her and pat her. We are just showing him he is important even if she needs something.