I'm sorry for the loss of two parents in such a short time! Wow.
I'd leave off the buttons. Tying will be quicker without them, but more than that, the quilts would be much more comfortable without them. No one wants to sit on buttons, or wrap little hard pieces of plastic around themselves to warm themselves up. If the quilts are to be strictly decorative, then it'd be okay.
We use polyester batting all the time in charity quilts (cuz that's all I have here that I know of!) and I tend to tie in about 6" distances. Sometimes it is 4" and sometimes even farther apart. So far now problems that I know of.