Grandparents Raising Children Support Group
This community is dedicated to grandparents who are the primary caregivers of their grandchildren. In cases where the parents are not willing or able to provide adequate care for their children, grandparents may take on the role of primary caregivers. Join the support group to find support, share your experience, and get advice from other members.
It's wonderful that you're thinking ahead, because it could be that you'll end up raising your grandson. I suppose it will all depend on whether his bio mom can continue to raise all five kids, and whether she wants to.
I know we would all strongly advise you to get full legal custody/guardianship (or whatever your state calls it) should you be asked or decide to take over. If both bios agree, you can probably handle the paperwork and hearing yourself, with no need for an attorney. But if even one of them contests it could get expensive. Again depending upon your state, you might have to find your estranged son so that he can be served with notices, etc.
I'd say keep coming back here to see what you could be facing, keep your eye on the domestic situation and prepare yourself by saving as much as you can now.