"We make an odd couple."
Translation:Nós fazemos um casal estranho.
Yes, saying "nós formamos um casal estranho" sounds much more natural.
We do talk like that. No problem.
Both "fazemos" and "formamos" are good.
"Nós fazemos um casal raro" was not accepted. My dictionary lists "raro" as a translation of "odd", so I reported it.
Why would "um par estranho" not work here? The English term "odd couple" does not inherently imply a married or romantically involved couple, which is what I understand "casal" to mean. It could be friends with widely divergent personalities, coworkers with very different work styles who have to collaborate, any of a number of situations that are not romantic in nature.