Should I apologize to my son?

My son lets me down time and time again. He charges me for jobs he does on my house and hiis partner agrees he should. I have his two children who are 3 and 4 who I love to bits twice through the week and they stay over at weekends. As I work full time I have said I cant do it anymore as its too much, my partner helps me with them, but on a weekend I am on my own. My son and his partner have given me an ulltmatum, I have them both or not at all. I have not seen my grandkids now for six week.I text my son saying that my nephew who died last year was more ov a son to me than he'll ever be. As I was a one parent family with my only son, my nephew would help me out and do jobs in the house for me. He never stood with his hand out wanting money for everything he did, like my son does. and he would'nt use emotional blackmail and use his kids to get his own way. I really am ashamed of my son who earns a fortune. Now he wants an appolodgy or he will never speak to me again. What do you think, I wont opologize im at the point now where i think my son is a selfish arsole.Am I in the wrong whats your views