G.M.
Hi H.,
I know you want advice on booster seats without mentioning buying a new car, but that would be my advice. Buy a new car like a Mini Van, or a SUV with a third seat. The reason being, is because when you cram your children, three of them, in the back of your car trying to fit boosters, car seat, and having seat belt extensions, makes for an unsafe vehicle to ride in. If you have a tight squeeze with your boosters and car seat, then your seat belts won't have enough room to react like they should if you were in an accident. Best wishes,G.