Barge cement works well for leather. It’s less offensive and easier to use (and still works) than some of the other contact cements. Ecoweld really doesn’t work at all, but it’s also non toxic, so… Contact cements are used in a lot of shoe and bag construction.
I also like Alene’s leather glue. It takes longer to dry and I usually stitch over it, but it actually holds fairly well.
CA glue will hold leather, but it makes it stiff and looks bad if it shows.
I have had occasion to use heat n’ bond iron on adhesive applique rolls in the past. I would recommend the permanent which is red. The purple is temporary. It does work but you have to use heat which is a little dicey with leather.
It looks as though you’re using stoned oil leather. If the tabs fold down, you might attach them to sleeves with sewing or rapid rivets for the nylon to pass through. I tend to use construction when possible to avoid relying entirely on glue, especially if there are stress points, but it might be enough. Let us know how it turns out.