What requirements do you ask for from your ex for overnight stays??

My ex has recently got his own place (after living with his aunt for 17 months). He wants to continue overnight stays with our 2yr but I have concerns. Some background, we broke up (his choice) because one of his daughters was very abusive to me and her siblings, including my lo. He said it was for my sake and the kids but his actions since then have not shown this. He has not lived with his kids since moving out and has only just got two of three of his kids back living with him. They were farmed off to his sisters and parents houses after the break up. One of his daughters (not the abusive one) ran away and went back to live with her neglectful addict mum rather than stay with her sister and grandparents. He has been having our lo overnight at his parents home since last November (after not seeing him for 7 months as he would not agree on set days or times for contact, wanting to only have him whenever he chose to) I only agreed to the overnights because he would be with 3 other adults and between them I hoped my lo would be kept safe and he promised to never leave his daughter alone with him. My concerns now are that it is just him and the abusive daughter there as his eldest son is out a lot and at work. This means that there will be times when she will be left alone with him and I’m worried she will hurt him again. She has hurt him in the past and both blamed him for it and shown no guilt or remorse despite him being only 13 months old at the time. He plans to let him sleep in her room on a trundle bed which again is a big concern as she is very protective of her space and will not appreciate him invading it. Further background- we did take her to see a specialist and they said that her obsession with her dad was unhealthy and that I was seen as her enemy because I stole her dads attention from her and that no matter what I did to try to bond with her or reassure her this view would not change without professional help. She has not got this help and as far as I’m aware is still the same towards her dad and siblings (hence her twin running away). What would you do if you were in my position?? My lo loves his dad a lot and loves seeing him but I just can’t help but feel really anxious. After all, she got rid of me and now she has finally got her dad to herself will she see my lo as her enemy??? Will she hurt him again??