Are you worried that it will be awkward to point out the weight differences? I can't imagine that
not being awkward.
At sea world a couple years ago the attendants made a man and his daughter leave a ride before it started because their size difference meant the bar was too loose on her. Generally, though, I think on the rides where it's most important, you will have individual restraints.
Are you going to Six Flags in Jackson? I lived going there growing up. Lightning Loops was the big deal in the 80s.