How many litters of kittens can Feral cats have in their life before they die ?

As long as they live. And as many times as they come into heat cycles. There is no real number to give you cause some cats live longer as ferels and some can have more or less then the average number of litters a year (3-4).

Call Ac and have Ac round them up and be desotryed. They spread dieases and parasties, slaughter wild life and damage proeprty

They start breeding as young as 6 months.. And can essentially get pregnant again within a few weeks after giving birth... So having a litter every 3 months isnt unheard of.
She will reproduce until death or spayed.. Whichever comes first.

Tell animal control to come and get them.

2 litters per year is common

https://calculate-this.com/420000-kittens-unspayed-cat-kitten-calculator

Its possible for a single cat to have more than 4 litters a year, but that is a pretty standard number.
Of course not all of the kittens make it, only a few from each litter actually survive to adulthood. Of those, a large portion will die with their first litter, as they get pregnant at 6 months or younger and can't survive the pregnancy.
Its great that you try to trap them, but its pretty easy for it to get out of hand. Call local shelters and see if they have a TNR program. This is when they come in, trap all of the cats, get them spayed and neutered, double check that they don't have any life threatening diseases, cut the tip of their ear off to show they are supposed to be left alone outside, then released where they were trapped. This way the cats get to live out their lives where they are most comfortable, but they won't be having any more kittens to make the problem bigger.

Call your local shelters to see if there is a Trap/Neuter/Return group in your area, so that they can assist you with the trapping. Have you had the ones you have trapped and altered ear-tipped so that you/they can tell who is who? Cats will breed around 6 months, and will have 3 litters a year. They breed until they die, sadly. Without help the situation will get worse for you and not better.

Female cats can reproduce two to three times a year, and their kittens, if they survive, will become feral without early contact with people. ... Example: A pair of breeding cats, which can have two or more litters per year, can exponentially produce 420,000 offspring over a seven-year period...... contact animal control or a feral cat rescue who will come and capture them, nueter them and if they are healthy and feral release them, if young enough to tame rehouse them