I have a small converted mini bus. It has 2 passenger seats. I left 3 seats in the back, well 2 just now as the third single is out to give a more sensible sleeping space.
Proper motor homes will normaly have the 2 captain seats in the front and perhaps 2 more seatbelts int he back at the dining table area. Sometimes you get an additional single seats too. But not likely to get more than 5 seats unless you buy a huge winibago.
I am using my van as my main car for now and use it a lot for work, not so much with kids. You really do have to think about how you will get out and about when away. A self standing awning is essential, you can leave it all set up with the contents inside. If you have to drive of you have to secure all the cooking stuff and perhaps put beds away to use seats and belts. Depends on the type of holiday you have, if you take bikes and get all supplies on site it fine.