Who forced them to skirt the rules?
If anything, I'd say if the brother felt pressured into skirting the rules, because they chose not to do the proper repairs and therefore had to have him remain on the title and insurance, the never truly accepted it as a gift and just used it as a long term loan anyway.
Given that the OP says they requested no gifts and that the brother had given them a BBQ already anyway, I imagine the "wedding gift" was just a one off comment (in one text message apparently!) meant to make offering the continued use of the car feel less like charity to OP's husband.
Along the lines of "we can't keep imposing on you like this. I feel awful. We don't have another car, but we need to be grown ups and figure it out"
"nah, I don't use the car anyway. If you need it, keep it--call it a wedding gift"