In grammar books, seu / sua can mean your, his, her, its or their — so a sua casa could be anybody's house. Everyday Brazilian Portuguese solves this simply: seu / sua means your, and for anyone else you use de + the person, placed after the noun:

Owner	Form	Example
ele	dele — his	o carro dele — his car
ela	dela — her	a casa dela — her house
eles	deles — their	os filhos deles — their children
elas	delas — their (all women)	a rua delas — their street
vocês	de vocês — your (plural)	o jardim de vocês — your garden

Dele is simply de + ele run together; de vocês stays as two words.