I agree with checking in with your mom to see what she feels she is able to do as far as bringing ds and than check in with the mom to find out if it is a drop off party or not. If it works for your mom to bring him, I would do that. If not, I would contact the mom and explain you really wish your ds could attend, but you are out of town. I would not feel badly about it if that is what happens; you tried, but you already had plans that don't allow your ds to attend.
lucky single mom to 20 yr old dd and 17 yr old ds through 2 very different adoption routes