If you don't mind SUV, CRV (3rd generation 2007–2011 model.. not sure about the current new one) is one of the v few cars that can have 2 child safety seats + 1 medium-sized adult sitting in the middle comfortably behind. The back row has a flat floor too, no hump in the middle.
I'm doing that. Actually took measuring tape and measured the backseats of Hyundai Tucson, Audi Q5, Toyota RAV4, VW Tiguan and Touran, Honda Stream, Toyota Wish ... all cannot (BMW 523i almost can, but not v suitable due to design of backseat, plus a big hump in the middle).
I'm using 2 x Maxi-Cosi Priori btw.. if you use Britax, you need even more width.
Any bigger you will have to go for VW Touareg ... same platform as Porsche Cayenne and Audi Q7. If go for Cayenne, have to choose the ones with ordinary seats, not the sports version. Quite awkward when I took out measuring tape at the Porsche showroom
Find out the measurements of your child safety seats... then the internal dimension of the car with allowance. This is because many car seats are not totally flat and have some curve/bulge at the sides. In that case, you cannot just push/squeeze the child safety seats all the way to the sides to make more space for the middle.
If you go for a regular 7-seater MPV like Toyota Wish/Honda Stream, once you use the 3rd row, there is basically not much space left for strollers etc. So a bit no point also.
Moreover, most probably you will have to put one safety seat in the 2nd row, and the other in the 3rd row. Don't think you can squeeze 2 safety seats in the middle, as one seat at the side must remain free so that you can access the 3rd row.