My friend made this kit and it turned out really cute. The buttons were sewn on just like any other button and didn't sag at all.
If you wanted to make sure they sat straight, you could stitch a small flat button on the back of the wallhanging and stitch the buttons through the same holes, similar idea to when you purchase a coat or jacket.
I don't know how to do a link on my ipad, but google reinforced buttons to get instructions on how to do the above technique.
Last edited by thimblebug6000; 10-24-2017 at 06:35 PM.