The words that we use to convey POSSESSION are pretty simple in that, we don't separate things by gender. In Portuguese of course, there are always two options: the masculine and the feminine. Portuguese possessive pronouns are a bit complicated by this and you just need to start trying to ANTICIPATE which form to use as you are speaking.
Saying my car and my house, for example have different words for "my" : meu carro / minha casa. While you're learning, just accept that you're going to get the gender wrong a lot. It's always better to just keep talking and try to correct yourself afterwards, than try to think ahead and speak perfectly. I see so many people getting literally stuck mid-sentence trying to remember the correct gender. Just talk! In time, and with practice you will gradually start getting these correct more often than not. You will never get ot 100%. What's amazing though, is that Brazilian themselves almost never (never) get the gender wrong. Their brains are hard-wired to the language from birth. They know that, and they don't expect you to live up to that!
Let's just talk about mine and yours:
meu / minha
seu / sua
The plural case it's simple - just add an "s":
meus / minhas
seus / suas
For his & hers things get a little more interesting. In Portuguese to say, his, they literally say "of his".
So for example: