Wah, your boys weigh 90kg, and they are only in the teenage years?

You shd have gotten a big MPV, not a compact MPV. I really feel sienta is a wrong choice.

IMO Sienta last row seats is useless for u. the 2nd row also very cramped, at best 2 of your boys can squeeze in.

U need a Toyota Estima/Alphard, Chrysler Voyager etc, those MPVs that a caucasian will buy, cause your family size (physical size) is huge.

I will not know what to do if in your shoes... mebe can talk to the PI (depending on what stage the purchase is) and upgrade your purchase to a bigger MPV. You really should have seen the car and ask your kids (or full family) to sit in before committing.