Help with mymusicstaff

So I saw some people recommend my music staff and I'm trying to figure it out and everything. I set a family as an auto invoice and it's $70 a month for four lessons. The family I added has three kids, but it says their invoice in $140 and the third kid isn't on the list of invoices. But then on the right it says they owe $350.

What did I do wrong? How do I fix it? I'm so confused.