General rule for snakes is you feed them food that is as wide as their widest dimension. If my snake at it's widest was the size of a toiletpaper roll, I should feed it rats that would fit inside the toilet paper roll or would nearly fit inside.
That being said, all mentions of BHP on forums say they act like they are hungry constantly, even if they recently ate. I would say what you are doing is fine for now. A lot of forums recommend splitting BHP meal into multiple smaller things when they get full grown to keep them from getting obese. I would say start with one bigger and two regular sized if you are going to increase portion size, but when you do I would be extra careful to watch for signs of obesity.
Here is a quote from a source I found here
The size of a meal for young growing pythons should be approximately 10% of the
snake's body weight each meal, and adults about 3-5%. It is better to feed two smaller
food items rather than one large item to assist digestibility. In the first year of the python's
life it should be fed once every 5-7 days. You don’t want young growing pythons to shed
more than once every 6-8 weeks. If they do, then reduce the feeding rate. Likewise if they
are only shedding once every 12-14 weeks, increase the feeding rate slightly. Adults
should be fed once every 2-3 weeks and it's fine for them to only shed 2-4 times a year.
Females preparing for breeding should be feed weekly. (Reptiles Australia Vol. 2 Issue 1 pg 6-
Keep in mind that this is specifically for Black Headed Pythons and isn't necessarily true for all species.
So if you want to weigh your food you can follow this. If your snake gets a lot bigger than it is now, then I would say to upgrade, but if it is full grown and isn't slimming down I would say you are fine.
As for the other snakes, they will need to upgrade eventually. The safest bet is to look at the care sheet for the species and see what others feed them and if all else fails feed to the snakes widest part every 5-7 days (for small pythons) and then increase the time interval between feeding when they grow more and take bigger food. This is usually done after a year or two of life when the snake is starting to reach its adult length.