Is it weird?

My mom was married to a man (we’ll call him M) for 13 years. We moved in with him when I was 8. We were never very close because I had issues with my mom and my biological dad and wouldn’t allow him to be a father figure to me. I was a very difficult child. When I was 17 I had my first daughter and she and I lived with him and my mom until my daughter was 4. When my mom left him, he and I got closer. He was obviously sad and lonely and my mom had cheated on him and disappeared for a while out of guilt. He clearly considered my daughter to be his granddaughter. I mean, she lived in his house for the first 4 years of her life and he was always a great role model for her. She loves him ! I’ve had two more kids since then. So, now I have my older daughter (she’s 9), another daughter that’s 4 and a son that just turned 2.

He comes over to visit once a week (he works 3rd shift or he’d be over more) and all three of my kids adore him.

My mom obviously doesn’t like that we spend so much time with him and he will occasionally keep my girls over night. He doesn’t keep my son yet because my son sleeps with me still and has chronic ear infections and is basically sick all of the time. He didn’t start keeping my other daughter overnight until she was 3 and that’s when he plans to keep my son over night as well. My mom told me that it’s weird that he wants to keep them over night and thinks it’s inappropriate because he’s not a blood relative. I don’t feel that way but I wanted to get some other thoughts. Is it weird or wrong for him to keep them overnight? They have their own bedroom at his house and the girls sleep in their bedroom together and he sleeps in his. They love him but now my mom has me upset.