There is a question in the rental income questionaire with a checkbox
"I converted this property from personal use to a rental in 2021"
I purchased a house in 2021 lived in it by myself for a month, in july I found a tenant to rent a room down stairs and in September I found another separate unrelated tenant for renting the room upstairs. During the entire 2021 which I owned the house I lived inside the house alongside the tenants.
Should I check in this box or should I not?
You should check that box, along with the one that states you are renting part of your home.
Since you are actually renting two separate spaces to two separate tenants, you may wish to enter two separate rental properties.