I am expecting baby # 4 in april at that time I will have a almost 7yo (bday in june) almost 5 yo(bday in july) and a 2 1/2 yr old. I want to be able to put the 3 of them in the back seat and keep a captain seat available for my grandmother who we have with us alot. I am thinking the 2 oldest will both be in boosters by then. Right now I have a harmony dreamtime booster, a evenflo maestro and a saftey first alpha omega elite. I know I will need to be at least 1 new booster and wondering if I will need a different harness seat? Not wanting to spend more than $100 per seat,anyone able to make 3 fit in a town and country?