The plural form for hyphenated compound nouns varies, depending on the type of word it is; for example:
I have two daughters-in-law.
We bought two T-shirts (tee-shirts).
It was found by two passers-by.
He does voice-overs for commercials.
No, the correct plural is fathers-in-law, a hyphenated compound noun.
Yes, usually hyphenated
The hyphenated plural spelling "thank-yous" is usually recommended.
There are two accepted forms of the noun: adviser and advisor.The plural forms are advisers and advisors.The plural possessive forms are advisers' and advisors'.
Verbs don't have plural forms.
plural forms are uteri or uteruses.
There are two accepted plural forms of the noun vertex: vertices and vertexes.The plural possessive forms are vertices' and vertexes'.
It can be, or it can be one word as in the question. Both forms can be seen in common use.
The plural forms thesauruses and thesauri are both acceptable forms of the word thesaurus.
The plural forms for the singular lumen is lumina or lumens, both are accepted plural forms.
There are two accepted plural forms for the noun cargo, they are cargoes and cargos.The plural possessive forms are cargoes' and cargos'.
Singular. Plural is: they are, have and do.