i think rather than telling off re: the toys/not wanting to play etc, it's better to be understanding rather than tell them off.
They don't have to share ALL the time - no adult shares their stuff ALL the time, so I think it's ok for older siblings to say no at times and to want their own toys. you can tell them that you understand the baby can be annoying, and negotiate with them, as in 'I'll play with the baby while you play with (whatever), then later maybe we'll play bubbles all together, shall we?' or something like that.
I think it's a bit of reverse psychology; kids who don't have to share all the time sometimes find sharing easier, funnily enough; if you always have a younger sibling in your face and in your stuff you get very territorial IMO!
So I think deal with most stuff by negotiating and making plans of what you CAN get them to play with together...if a child is taking toys off the baby, get them to decide what they WILL give the baby that they don't mind handing over etc
If it's hitting then obviously you need to not ignore that, use time out or whatever, but I don't think you need to continually tell them off - just a NO, then the consequence, then move on.
HTH