Could my partner only carry one sex

Hey ladies, so me and my partner have 3 gorgeous little boy and wouldn’t change it for the world, I come from a background of just girl in my family on my dad side, and my partner come from a back ground of 5 children, him and 1 of his brother have the same mum and dad, and the other brother and sister have different dad and his older sister has a different mum. I was wondering what are the chances of having a little girl 4th time lucky? Or is he just a carrier for boy sperms?

Are there any tips on to increase our chance of a girl?