Stroller wagon

We are expecting baby 3 in May and I’m looking at stroller wagons (they are so expensive 😭). I’m wondering if anyone knows if the two seater (two seatbelts) could fit a third child in the middle unstrapped. My oldest will be 4 so she doesn’t need a harness, just need to know if there’s room.

I looked at the four seaters but they are so much more expensive. And the two seater I’m looking at has the adapter for the infant car seat which I love.

Any recommendations or advice would be great!