I feel that you must discuss the detail with a professional person who has experience in this field, and who can take it further if it is needed. If this man has a history of bad relationships and parenting, then he is probably known to the social services in his area. Whatever you say will be treated in confidence, and checks discreetly made.
Meanwhile, do all you can to build up your grandson's self-confidence, and let him know that you are love him and will be around to listen to him. Keep lines of communication open with your daughter without ranting about her choice of partner - as you say, it is her relationship and her choice. It is possible that she may see him with different eyes once the initial rose-tinted spectacles wear thin, and she will need you then.
Good Morning Good Friday 29th March 2024
Son on rebound - wants to marry