I think it's useful to try and remember from your DS's point of view that his world has changed, utterly, but he needs to know that the way mummy feels about him hasn't. That's why he's playing up, for attention, but you probably know that. I second the one to one time, during naps or whatever, or if you can leave baby with someone for an hour to take DS for treats, to the park or whatever.
If you can work on building the bond with the siblings it might help things a bit, if your baby is smiling if you can point out to your DS when she is smiling at him "look, she likes you", or "look, she's watching you" at meals, playing etc. Focusing on the baby being "his sister" and not "the baby". The Sibling Rivalry book from the How To Talk So Kids Will Listen people was quite interesting, as was another one, Raising Happy Brothers & Sisters. If you have time or energy to read, that is!! One of the things that sort of helped us was baby had some toys of his own (genuinely his own, we told DD it was DS's frog, etc) and DD has toys of her own but wants to play with baby's, so we tell her he is letting her have a turn with them, and then "shall we give them back to DS?" when she's finished. She seems to understand that at 2yrs and so far is quite "kind" with letting DS take turns with her toys too, although we never push that, she's taken it on herself to reciprocate. And she gives him his toys when he's crying, it's quite sweet really. For the most part, they get on well so far.
Distraction is my biggest tool at the moment. And not dwelling on the 'bad' - DH will tell DD not to do something and spend ages going over the point of conflict, which makes it a bigger deal, whereas telling her not to do that because (insert reason), and would you like to come choose a book to read instead, tends to work better - if she says no, then I say "really, not even (title?) Or (title?)" Sometimes she'll then engage in the alternative activity, or sometimes I'll keep up the dialogue but do something silly with the book, like put it on my head and say "is this how we read it?", anything to keep her mind off what she wants to do that she can't/shouldn't. Or if she does do something she shouldn't, telling her why she shouldn't have done it, but not giving her loads of attention for it, giving her attention for something else more positive. Make the point and move on. I will take things away if they are being used to hit with, but explain why ("because you hit me with it and it hurts mummy and gives me a bad bump, so we need to play with something else now" - possibly not strictly UP though) and distract onto another activity.
Sometimes she does things she know she's not supposed to and I am struggling a bit with that so I probably need to find some new ways too! (She says as she nurses a sore nose from being hit with a cup this morning - although that was a result of too much TV and cabin fever from being cooped up with poorly DS and a listless me from being up all night with DS. She did say sorry afterwards, so I cling to that as the message getting through, but if she'd not done it in the first place would be preferable. I'm starting to talk to her about her feelings and using words rather than hitting but it's a little early for that still I think. I do tell her we don't hit people, if we want to hit, we hit drums though.)