1. The Posessive
MY, YOUR, HIS, HER, THEIR are English posessives but their French singular equivalents indicate the gender of the object owned, not the gender of the person who owns them.

2. There is only one form of “my” in English for singular and plural, but…
In French a car is feminine: Une voiture so I say “ma” voiture
Un frère (a brother) is masculine so I say
“mon” frère
BUT if I have several cars, or several brothers I say “mes” voitures and “mes” frères. Note the
Presence of an “s” to pluralize most nouns.

3. “Tu” or “Vous”?
If I know the people well, or if I am related to them, I use “tu”, so I use “ta” voiture, “ton” frère, “tes” amis / “tes” amies (your friends, males or females)
If I don’t know people well I say “vous” whether there is one, or several people, so I use “votre” for a single object, “vos” for several

4. HIS / HER
In English you think of the gender of an object’s owner to express posession
In French you think of the gender of the object itself and every single object has a gender that you must learn with the noun itself
Paul’s car, “his” car is la voiture de Paul, “sa” voiture
Marie’s brother, “her” brother is le frère de Marie, “son” frère

5. Their: Leur / Leurs
In French if a couple owns one car it will be “leur”(their) voiture. They will say “notre” voiture (our car)
But if they own two cars it will be “leurs” (their cars) voitures. They will say “nos” voitures (our cars)
Speaking to them, I will tell the first couple “votre” voiture est jolie, but the second couple “vos” voitures sont jolies
Note the verb and the adjectives in the plural in the second case.