You just have to find a way to be firm about it. What’s your partner’s job, would they like it if you came and interrupted them there?
We actually had to make a rule, if my office door is closed, I’m working. Most people don’t have an office, but some physical sign that you are on the clock might help. Also, removing yourself from the location when possible might be necessary.
People don’t realize how disruptive it is to stop someone when they are on a roll, writing. My mother in law used to call and gossip sad news about people I don’t even know, and it would take forever to get back to where I could write funny dialogue. You can’t let people steal your time like that.
You have to convey how important this is to you. It’s not a hobby, it’s a career, it’s a calling. It takes effort. You need their help, and the best help they can give is letting you work.
Good luck.