First check the oil: post picture of dipstick if you are not clear how to read it. If low top up oil ideally with the correct grade but if you cannot get that any engine oil is better than none.
water. Top to full mark on coolant bottle.
now look under car to see where water and oil are leaking from
As to garage. Ask your friends who they use and trust. Generally stay away from the national tyre chains- they are good for tyres but that’s it
Sounds like head gasket. That sucks man but if you can prove somehow that the issue was there prior to the end of warranty you could still get it repaired under warranty.
If you run the engine for a few mins, let it cool for 10-15 mins and then pop the oil fill cap off, is there like a creamy residue on the underside of the cap? That is the number one sign of a head gasket issue. If your exhaust comes out blue (I think it's blue, might be white but either way you'll notice a difference because you shouldn't even see exhaust fumes in the summer) then that could also indicate a HG issue.
Do you have any leaks under the car? Anything dripping or pools of liquid in the undertray (these will spill out during a drive, so look for water marks on the bottom of the undertray)?
The fans are going because the car doesn't have enough coolant by the end of the drive. So that coolant is going somewhere, just gotta figure out where.