"Where are you going over the holidays?"
Translation:Ble dych chi'n mynd dros y gwyliau?
Surely when asking "where are YOU going..." it should be on YOUR holiday. Eich wyliau. That is what I am being taught by a Welsh speaker.
Yes, you could say that to refer to your particular holiday:-
Ble dych chi'n mynd ar eich gwyliau? = Where are you going on your holiday(s)? (no mutation after eich)
This sentence is a bit more generic and refers to national holidays or more often a shared break from studies or work, especially summer.