Daugther's boyfriend not biological father tho her son,can he legally prevent us the biologicalgrandprents from seeing said child?

Our daughter boyfriend who is not the bioloical father of her two year old son is trying to prevent us the bioloical matrual grandparents from seeing our two year old grandson,is this even legal?we think not.We have bent over backword to make him welcome into are family but all he wants to do is arugue with us over stuipd stuff,disrespect us,use vulgarities trowards us,and just plain being a jerk.He seems to have a real problem with authority figures.If only are daughter could see him for what he really is would be great!what should we do?what would you do? We just want whats best for our grandson so he is not stuck in the middle of all of this while mataining a close family realationship between our grandson and are daughter.We feel the boyfriend needs to stay out of our buiness and we will do the same for him.even though we have not done anything to him except be nice to him for are daughter and our grandson.