maybe if you make them a ruler and try to marry them like any other ruler. I have never tried that so don't know if it actually works, just a thought

If you marry your companions in most mods it doesn't even show that they are married to you. I believe this mod is the same. I never marry a companion.

Marrying male companions as a female character I think is ok. On one playthrough I married Shagga and on another Barristan. Female companions are a bit weirder as I tried marrying Val as female character and although the option to propose was there it didn't work. She kept saying the whole, "another maiden has captured my heart," line even though my faction had no ladies. Which is strange since most mods like Pendor which allow male companion marriage but not female ones typically just remove to dialogue choice entirely for the latter. I think the whole weirdness is due to female lords being treated like male ones.

So overall, male companions yes, female companions idk but might be possible.