Hiring a car with three kids

[DustyDoorframes]

I know three is not exactly a large brood, but as fitting 3 car seats across the back seat is not a given, how on earth do you hire a car (ie- "medium, such as x car", so mystery model), and be sure you'll fit???
We have our own car seats as I really don't trust the ones you hire. We've got a baby in carrier, a preschooler in a high back booster, and the eldest MIGHT now be big enough for a backless booster, which would make it easier.

We've rarely had to hire cars before, but would rather do that over getting the train to visit grandparents just now. It's doing my head in!

Get a 7 seater. Always fits. and you have more room for stuff.

You need 3 separate seats in the back to accommodate car seats.
S max
Galaxy
Touran
Sharan
C4
Google what cars have 3 separate seats in back and it gives you other models.

@MollyButton but even then it looks like some 7 seaters don't actually take three car seats? (And they are so expensive! And huge for someone who rarely drives! Which I know makes me an awkward besom and I'll have to just get over it...)
@poorbuthappy But that's my issue- no hire company will commit to telling you exactly what you will get. Do I just book and hope I get the model they use as the example?
Thank you both for your replies! I may well be overthinking this...

What 7 seater doesn’t take 3 car seats? Unless they all need to be Isofix or something? I have a grand scenic, I can definitely fit 3 car seats in it.