I am on a student visa in the UK. My sister wants to visit me for the summer and she wants her daughter (8 years old) to go to an English course (like 1 month) while they are here in the UK. I went through different visa types and I am really confused now. it seems that one option is short study visa but I am not sure of the age limit for that. another option is tier 4 child visa but it seems to be limited to the children who want to go to school here. another option might be the standard visitor visa! you can see that I really do not know which category we should go for.
also, which type of visa for my sister and her other baby (2 years old) and my brother in law as well. should they apply for visitor visa!
please help me on this which looks more complicated than my PhD

Many thanks,
Mostafa