Pictures would help.

When females don't spawn their body reabsorb the eggs. Only once in a great while this doesn't happen and the eggs become what's called impacted.

But there are other causes that can result in the described shape and size. The most common cause I've seen is a build up of fluids. Fish can have a hard time balancing fluid inside their body because they live in water. If they have a problem with this fluid builds in their body cavity slowly (months, years) and at some point they get so round they can't even swim. Up until that point they eat just fine. When I've finally had to put them down and cut them open to learn the cause I found nothing but a big void in their body cavity full of clear fluid.

There is also something called dropsy or pine cone disease where the fish bloat up so fast their scales don't lay flat and point out like a pine cone. But this isn't actually a disease it is a symptom. So any web site or person that tells you how to fix this "disease" should be ignored. It's like saying your finger hurts and based on only that someone telling you how to fix it without know why your finger hurts. Cut, broken, arthritis, dislocated, etc. would all have different treatments. Same with dropsy.

I see people often guess constipation in forums. A bad guess. For constipation to cause the size described the fish would have died long ago.

One symptom that stands out is having so many fish with the problem. Makes me guess water quality issues.

Cures
I've never found a cure for fluid imbalance. Some people say to use salt but I never saw any change or ever read of anyone ever having any success. I chalk that cure up to some people say salt to fix everything.

Things that cause dropsy are pretty hard to actually cure. Your best weapon imo is the fish's own immune system. You may be able to boost that by making water quality the best it can be. That's a book by itself so I won't get into it now.

For curing egg impaction the idea is to either stimulate spawning or absorption.

For absorption you stop feeding and as the fish's body looks for energy it will turn to consuming the eggs. This can take more than a year.

Stimulating spawning involves messing with water temp and chemistry. I assume the water is already above 75F, but if not you can raise the temp to 75-80F. Changing the water chemistry would be something like having another large tub and filling with fresh water and moving the fish into that tub and also having spawning mops and males in there. Spawning can happen almost immediately if the females are able. Egg impaction can prevent spawning so you then net the fish and gently try to push the eggs out. Just lifting the fish out of the water can be enough, but a few light strokes may be needed. This is called egg stripping. Obviously you don't want to be so rough as to kill the fish. Unfortunately to learn this you may have to kill a few fish...Catch-22.

I think the best course is just create the best water quality you can and stop feeding or scale way back. That covers a lot of bases. There's always a Catch-22 in these cases. In order to really cure fish a person really needs a lot of experience and if they had that experience they would already know what to do. Catch-22. So I think the best way to gain experience is to start with water quality. It gives you the biggest benefit for the least amount of work and learning.