Don’t trust SKs with my baby

My step kids are early adolescents. I have a 7 month old baby with their father. And I do not trust them unsupervised with the baby. And I feel badly about it but I want to follow my gut. The oldest boy is lacking some common sense. There have been a few times he has done things which I feel are inappropriate, for example he had his fingers in my daughters mouth, he was shaking a loud toy close to her ear, this AM he was playing with her with a little truck and wanted her to catch it and was going to shoot it over and I said no don’t do that she can’t catch… just things that I feel like are obvious to most that they shouldn’t do with a baby.

The daughter has always been a bit aggressive, and even malicious, mostly directed toward her brother, but her comments to me and her dad are often intentionally hurtful. She said multiple things while I was pregnant that made me nervous (silly but one I remember was she is going to launch the baby into space).

Due to these factors I am just not comfortable leaving them unsupervised, even for a few minutes. My husband trusts them.

Also, shes crawling now and getting into things. She legit needs to be watched,