How do I prove i was under kinship care if it was informal?

Basically I did my GCSEs in wales under care of my aunt..and i was with her for a while and it was informal, but my dad lied and said my aunt was my MOM (cuz they were scared CPS would get involved or smth) so..does this complicate things for my uni application?
How do I get proof for things like this if it was informal (I plan to go to Manchester University)