in my group there’s clearly a female, but my biggest male just not interested her but always following another male and mount him all the time, so is it that mean that male maybe a female?
OK. Well if you have seen that tortoises penis, then that settles that.
So, yes....males will often mount other males. They will push each other around, circle each other, etc... as they set dominance in the group. Since you know the smaller animal is a male, I would suggest you separate him from the bigger male. The smaller male is not having a good time with that bigger guy raping him all the time ;-)
In fact, I would keep them all separate from each other. (since you have 2.1)
I would then put the big male in with the female for a few days, then separate them again. In my experience, the males get bored with females in the same enclosure. Separate them for a while, then reintroduce and you might have better results.
Is the female an adult? at least 10 years old and 12" or longer SCL ?