Hvala. Wow. My brain is full. Haha.
Quick, copied, notes...
mine: moj if you say: Moj klavir. moja if you say: Moja flavta. (a female word), moje, if you say: Moje violončelo. And : moji if you say: Moji bobni. (plural)
so it's: moj (and you add: -a, -e, -i for female or neuter or plural) and it's the same with all others too.
So:
Moj (a,e,i)
Tvoj (a,e,i)
Vaš (a,e,i) (that's formal your)
Njegov (a,e, i) (his)
Njen (a,e,i) (hers)
Njegov (a,e,i) (its) -the same as for his
Naš (a,e,i) (ours)
vaš (a,e,i) (yours)
Njihov (a,e,i) (theirs)
And also for pairs:
Najin (a,e,i)
Vajin (a,e,i)
Njun (a,e,i)
Hmm...
Moj klavir je crn. Ja?