School related question

I just have a question. Idc what kind of criticism she gets bc ik she’s wrong but my mom has yet to enroll my younger brother and sister in school. Like EVER. My sister will be 11 in august and my brother 9 in December and they have NEVER EVER been in school. It’s like she just doesn’t care or bother to enroll them. They play outside with the neighborhood kids but other than that they’re at home. All the time. Not even getting home schooled just no schooling at all. My son will be 4 this coming school year so I’ll be enrolling him. I was jw me as their sister ; do I have any right to enrolling them on my own or how do I go about doing this ? We ask her every year to enroll them and she has excuse after excuse as to why she’s not or when she is. I’m just sick of this and clueless as to what to do. I’m 20 my husband’s 21 and we only have the same mom different dads if that matters at all. My sister can BARELY read and I don’t even Know if she can write and she still talks like a little tiny kid. It makes me sad.

***We’re in Texas ***