I currently live in Florida and am a divorced non-custodial father. I am planning on moving to pa (have to for job reasons) in the summer. My 2 kids are going to come with me when I move and then move back at the end of the summer. The kids are 8 & 11. My oldest wants to move with me for good but my youngest is not sure. If I have custody of them during the summer and they decide they want to stay with me in PA can I keep them in PA and request custody of them? What if only 1 of them wants to stay? Would is still maybe be able to get custody of both?

No you cannot keep custody of them until a court awards you custody.