Can I sue my sibling over a train collection that was handed down to me from my father? If so, what type of lawyer would be needed?

The answer to "can I sue" is always yes, but the question is how strong is your case.  You say the trains were "handed down."  What does that mean?  Did your father leave them to you under his will?  Did he give them to you before he died?  Assuming the latter, can you prove it?  If your father did not give them to you before he died or leave them to you in his will, they would have passed to whoever inherited the residuary of his estate (the part left over after specific bequests are satisfied), presumably your mother.  If so, what if anything did she direct regarding the trains, either in her will or gifting them before she died?  What I'm getting at is that you may not be able to prove that the trains legally belong to you.  Another issue is the statute of limitations.  Your sister has had the train collection for years.  You would have a finite amount of time to sue her to recover them; I don't know the exact period in Pennsylvania, but it sounds as if a great deal of time has passed.  If you had an agreement that your sister could keep them until her kids reached a certain age, and agreement which was only breached a short time ago when the kids reached that age, you would be within the limitations period because her wrongdoing would have occurred only recently, but if her wrongdoing occurred when she took the trains years ago, your claim will probably be barred.