so i'm a newb trying to learn as much as i can and prepare myself to hopefully within the next year to two to start breeding. i'm in the process of building myself a rack and making plans to isolate a small room for regulating temps. i feel like i'm getting all my ducks in a row except one detrimental thing..... with all my practicing over the months, i still have been unable to successfully pop any of my balls. I currently have two females and three males. i know the males are males, the breeder popped them in front of me, ive had sperm shed come from one of the males, i NEED to know how to sex the snakes if i'm going to breed. i cant just rely on other people to do it for me or just assume someone is telling me the truth about the snake. tonight was the closest i had ever gotten to popping them but i'm still not seeing any hemipenes. i've watched numerous videos for sexing and try a couple times a month..... maybe i'm not squeezing the tail hard enough? should i give up before i hurt the snakes and just opt for using probes? i heard that it is very easy to damage a snakes reproductive parts with a probe if you don't know what you're doing....
i know that generally males have longer skinnier tails? but that's not a definitive enough tell for me.
so this is what i'm doing.
i place my thumb on the cloaca scale and pull back so i see the pink. i place my thumb about a thumbs width from the cloaca and roll my thumb up towards the cloaca. i've gotten to the point with one of the males where i saw little lumps for the hemipenes but they didn't pop out like they did when the breeder did it for me.

any advice would be greatly appreciated. i'm getting pretty discouraged.
i feel like i should mention that my females are both around 2 yrs old. the males are 2 that are about a year and one that is probably around 8 months.