I'm concerned about my homeschooled nephews

I'm an auntie to two boys, 11 and 6 but don't have any children of my own or spend time with other kids so I am a bit clueless. I want to know if my concerns are founded.

My sister took her oldest out of school a few years back (youngest never started) and has been homeschooling them. The oldest recently showed me their notebook and I was concerned to see that they have not yet grasped punctuation, and that many words were misspelt. So much so that I struggled to understand it. He was also telling me that dinosaurs aren't real.

I've asked polite questions in the past about their homeschooling but they were always met with annoyance. When I expressed to my mum (their nan) that I was worried they would fall behind she got defensive and angry so I've never gotten any feedback or insight into the situation.

I'm hoping that this is normal for an 11 yr old, please could you let me know?