Would you do it?

This is long sorry

My sister and her 3 kids and boyfriend(also kids father) live with me. The kids ages are 11,9,7. The 11&9 have not gone to school yet this school year (i asked them and they said they haven’t gone to school yet). The 7 hasn’t even been registered in school I found this out by questioning the kid and they stated they’ve never been to school. I was not aware of this situation as I’m out all day at work then after school activities with my kids so I don’t get back home until late. I came to find out when I installed cámaras at the entrance and around outside my house and noticed the kids don’t ever leave the house. So I questioned her and she gave me this lie that they were doing virtual - because she kept them at their old school district she thought I believed it. I didn’t! So I have been pushing her more and more and she has yet to do anything about them going to school or seeing a doctor. So I was talking to my best friend about it and she suggested I take guardianship of the kids just so I can enroll them in school and take them to doctors appointments etc. because I don’t think these kids have gone to a doctors since before they’ve moved in here back in The end of 2020 ( I think this for a reason I don’t want to share).

** I forgot to add the boyfriend works all day and when he is home he just sleeps (kids words) I have tried pushing the boyfriend about sending the kids to school or to see a doctor and all he says is “well I’m at work all day she has to do those things”

so my question is would you guys take guardianship of the kids or just not do anything at all?

I’m at a loss as she is my sister but she isn’t doing right by the kids