We have a 7 and a 9 and both are awesome. We had a 3 before the 9 - tragic Mazda lovers

The 7 fits 3 car seats but just - it's a squeeze. The 5 looks smaller but is supposed to be the same size so should also fit 3 car seats but narrow seats would be a good option.

Friends of ours have the 5 and are very happy with it and it's comfortable with their 2 kids. It does look smaller than our 7 though Check measurements on the Mazda website.

We love our Mazdas though, would highly recommend one. If the 7 is actually bigger then I'd opt for one of those instead. You could probably get a good deal on a second hand one these days.