Oh, I get it.
Yes, "am" (the letter mem) turns a word into "their" [word]. It doesn't have a space, so it'd be mariam (îøéí). That would be pronounced meh-ree-AHM, not like Miryam. Because of that, and because that sort of expression doesn't generally fit in with normal naming practises, I doubt this explanation.
And adding "-am" functions only as "their" (the male their - that is, plural, with at least one male) - the other pronouns each have their own form (if you want, I'll list them).
And as for marar: I don't know the form, so either it was used only in the Bible or it doesn't exist. But I think it would be îÈøÈø if it exists.
How do you make Hebrew script not appear as gobbledygook?
Noa