possessives

Masculine Feminine
singular plural singular plural
My
mi mis mi mis
Thy (unused)
tu tus tu tus
His/Her/Its/Vd.
su sus su sus
Our
nuestro nuestros nuestra nuestras
Your (unused)
vuestro vuestros vuestra vuestras
Their/Vds.
su sus su sus

The gender of the possessive word is determined not by the sex of the owner but by the gender of the thing possessed.

We should translate a thought like "my house and yours" as "my house and the one of you", and say: mi casa y la de Vd.

To translate a phrase like "Your house and mine" we would say su casa y la mía, or, better, la casa de Vd. y la mía.

Masculine Feminine
singular plural singular plural
Mine
mío míos mía mías
Thine (unused)
tuyo tuyos tuya tuyas
His/Her/Its/Vd.
suyo suyos suya suyas
Our
nuestro nuestros nuestra nuestras
Your (unused)
vuestro vuestros vuestra vuestras
Their/Vds.
suyo suyos suya suyas

Sometimes mío, etc., is used without the article, e.g., la casa es mía.  When the possessive has before it some part of the verb ser, used with the idea of ownership, the article must be left out.  The article must be used with estar.

Mío is also used for emphasis or contrast.  "He is my friend" can be translated as es mi amigo. But to emphasize he is your friend, not someone else's, use mío AFTER the noun: es amigo mío.

The phrase "of mine" is generally translated without the "of".  "A friend of mine" would be un amigo mío.  "One of his friends" would be better translated as un amigo suyo than by uno de sus amigos.