A friend of mine had a similar situation - 16 year old daughter, impregnated by a guy he considered totally worthless. Being a Catholic family, there was no question about having the baby. Also, giving up the baby for adoption wasn't much considered. However, to give his daughter undiminished options, he and his wife adopted their granddaughter as their daughter. I found that an amazing response to a problem situation.
Not for a moment am I suggesting that you take my friend's solution. In his shoes, I would not have.
Grandchildren are a delight. I have one of each kind.