Yes you should drain them some at least because as they thaw much of the liquid will be water not syrup from ruptured cell membranes and the ice crystals that form. If not drained you will end up with very thin syrup. How much? Cant say as that all depends on the type of peach, how long they were frozen, the size of the cut pieces, etc. If the recipe called for peaches only (no juice) then drain them completely. If it also calls for juice then save that much when draining.

So you will have the choice of making the syrup with less peaches OR opening additional peaches to make up the difference. For future reference when freezing in pre-measured amount always include a bit extra to make up for what the thawing costs you in amounts as ALL soft frozen foods lose some weight when thawed.

Dave