I would strongly suggest that you seek the advice of an attorney in the area as soon as you can.  Your son is an adult and his girlfriend a minor.  The situation could be a legal nightmare for him criminally and you need to understand the issues clearly.  Now, aside from their ages, if they are not married then she is the only legal guardian of the child until parentage is established.  That would generally be after the child is born. I might suggest that it is in the best interest of the Mother and child not to be involved with the other grandparent at this stage as she seems to be in a difficult frame of mind.  Seek help.  Good luck.