In your polymath there is the tier of
This needs tending too. A Shared Sweetie person (you) does not exist solely
to care for the partners in those other relationship tiers. Have to tend to self too!
So why can't you just say to them:
" I need some quiet time alone to work in my room. I have to clean it too. Could go clean your part of flat. Then everyone is cleaning and taking care of business. Whee! Chore solidarity for the polyship! Love you! See you at 6 PM for dinner. Now shoo! Work time for me!"
The other option is fine... your bedroom with the big bed is now the shared polyship bedroom. Can you have THEIR room then for your work office? Then you could say
[INDENT]"Bye sweeties! Going to work at the office! Will come home for dinner at 6 PM!"[INDENT]
And shut/lock the door and "go to work."