Oh, these are such good questions.
Given the questionnaire structure, I think the owner/renter information is limited to the status of the primary householder (and therefore everyone in the house would be in an "owned" household, even if they're a roommate, boarder, etc...):
Is this house, apartment, or mobile home –
Mark (X) ONE box.
_ Owned by you or someone in this household with a mortgage or loan? Include home equity loans.
_ Owned by you or someone in this household free and clear (without a mortgage or loan)?
_ Rented?
_ Occupied without payment of rent? âž” SKIP to on the next page
www2.census.gov/.../quest24.pdf
Even if the person filling out the survey rents from the primary owner, the question structure refers to whether or not it's "owned by your someone in this household..." And there is only one set of cost questions (one for if rented, one for if owned). There's no place for each person to list their housing costs.
Person 1 should be responding with rent for the entire household. The question wording is:
What is the monthly rent for this house, apartment, or mobile home?
(Whether or not everyone thinks to report that way is unknown, but the instruction is rent for the house, not personal/individual share of rent.)
Yes to the 4 roommates being one household with 4 unrelated individuals.
Housing cost burden is calculated for the entire household (all housing costs and all income pooled).
On median rent... I think the question structure is getting at something like "market" rent--what a unit might be listed for, but doesn't allow for analysis of individual cost burden in cases like you've described. (But maybe I'm wrong and there's some way to tease that out of the data that I'm not thinking of? Would love to hear thoughts from others!)