I get an error with northern living allowance that both people cannot claim both amounts. Only 1 person is claiming both does that same person has to claim rent as well?

I'm sorry but if one is claiming this travel expense, then the other cannot.

Quoting from the CRA website - "You cannot claim a deduction for travel benefits if:

• you or any member of your household received or was entitled to receive non-taxable amounts as travel assistance, a travel allowance, or as a reimbursement for travel expenses; or
• someone else has already claimed the deduction for travel benefits for this trip on their return."

This is from the link below directly from the CRA:

Line 255 - How much can you claim as a deduction for travel benefits?