i've been there, so I can sympathize. Thankfully all mine are school-aged now (one is even in college!)... but now I have a 96-year-old father in the house, which in some ways is worse. He can't seem to understand that when I'm writing, I'm working, and that my writing helps pay the mortgage that keeps a roof over his head. When he wants something, he wants it
now, and when he has a question, it has to be answered
now. If I don't drop everything and pay attention to him when he wants me to, he will sulk and get cranky. This wreaks havoc on my concentration. It's almost like having a toddler again.
I don't know what to tell you, except do your best to write in the brief quiet times throughout the day. Even when you feel like you're not getting anything accomplished, if you type a few sentences every time you have the chance, you'll be amazed at how much you get done in a day.