2x mtbs fit in any polo with wheels on easily
Wheels on, no way.
My last car was a previous generation Ibiza, so potentially the same chassis as the OP’s Polo depending on how old it is.
2 bikes, all wheels off with sheets/cardboard between the bikes to protect them & a couple of bags of kit thrown in, is perfectly do-able.
I’ve had 3 bikes in the back of my older Fiesta without too much bother (again, bikes with wheels off – stack frames with protection between & then wheels on top in bags), but that was when taking a second car that carried all our bags/kit.
I built a stand for my bike to put it in the back of the car vertically, with wheels off & seatpost out. There was then loads of room for kit & you only had to drop part of the rear seat.
We did manage once to get two bikes in like this by lashing another frame to mine with bungee cords, but I wouldn’t want to regularly do that.