Need car seat help

I have a 2013 Buick Enclave. We are taking a road trip to Williamsburg, VA and I will need to put both my car seats in the third row because my niece gets car sick if she's in the back. My older DS is easy because he's in a booster. I moved my younger DS car seat and there are no latches back there, so I installed it with the seat belt. It's definitely secure. I do have a top tether on the seat, but there's nowhere to attach it. The only tether for the third row is in the middle and the seats won't fit next to each other. Plus I need some space between the boys.
Am I ok with just the seatbelt? I certainly wouldn't want yo do something illegal or unsafe, but it genuinely feels very tight and secure.

Need car seat help

Can you check the manual for the car. It should give info.

Need car seat help

How come you can't leave one car seat in the second row with your niece and have your older with the booster in the third row?

Re: Need car seat help

Re: Need car seat help

Assuming your car is equipped for a belt to handle a car seat (and I'd imagine the majority of cars are), the seatbelt is no more or less safe than the latch. I have mine installed with a seatbelt because I wanted her in the middle of the car.