Yes and no.
They're real princesses, as in they're 2nd and 3rd in line for the throne of Zephyr heights. But they're basically elected officials since the ponies of Zephyr heights had no problem kicking them to the curb and threatening them with jail time for pretending they could fly.
Meanwhile alicorn princesses have nearly goddess like power and immortality and wouldn't exactly need anyone's permission to rule.

okay.

if zip and pip went back in time (looking at your doc hooves) will they be able to fly? or not?

They will have no trouble flying as there is TONS of magic around in the mlp: fim era!

but they are from future and in future there is NO magic, and since they from future they won't be able to fly.

There's no good way to test that.
They could fly in my little pony: tell your tail. (YouTube shorts,) so does being exposed to enough magic "fix" flight or do they have to go through a transformation?
I don't know.

okay, i haven't seen the shorts, or mym yet. but i gotta check them out at some point.

They are just ok. The animation is a little rough...