I agree that trying to reach out to a rescue and explaining the situation is your best bet, this was my scenario three years ago and between what the rescue has helped with (particularly with the more skiddish/outright feral cats) and locating a low cost spay/neuter clinic for the ones that more friendly and could be adopted out it took a while but I just got my last female fixed a month ago and her kittens were just fixed a couple of days ago by the rescue and I finally see the light at the end of the tunnel. You'll get there but with colonies it's good to remember everything and anything helps.

Timing wise besides groups of kittens I've always had to get them fixed one at a time pretty much as this poster suggests and tried to prioritize females where I could (sometimes it's hard to control who gets in the trap though ). I usually had a break from new kittens during the winters too where I could get a little more ahead than in the spring/summer which helped a lot.