Oh crumbs more than one piggy with bloat will be hard work!
Is it gas bloat (sounds hollow when tapping the stomach area) or liquid bloat (all squishy/sloshy like a hot water bottle)?
As it will need slightly different treatments.
Liquid bloat - will need diuretics quickly to reduce the amount of liquid in the body.
Gas bloat - will need the excess air to be dispersed, please get them to a vet ASAP.
Bloat of both types can be a life threatening condition.
Take the boys off of all veg for the time being, just stick to water, hay and pellets.
Check the hay and pellets for any contamination in both (mould, plants other than hay in the hay, foreign objects, etc.).
The vet should give you gut mobility drugs, I think zantac & ranidine? )are popular in the UK. They'll need one for the lower & one for the upper parts of the digestive system to keep the food moving through. Helping to prevent gut stasis & further bloating. Try to feed them some mushed up pellets in hot water (cooled slightly before feeding). Just to help the digestive system have something going through it, to keep it going

.
It may be the celery that's causing it if they haven't had much veg lately.
Its a bit like humans having cabbage/sprouts occasionally, we'd be blowing the house down with the sudden excess of gas!
If you can massage their tummies with an electric toothbrush, your hands, vibrating pad if you have one, or pile the boys into their pairs into boxes & put on top of the washing machine on a spin cycle to vibrate the air out, until the vets appt can be helpful as u have so many affected.
Gripe water from the supermarket baby aisle/pharmacy can help disperse the gas too, but speak to your vet first.
The boys will be fine with no veg for a bit, but make sure when they've stabilised you only add 1 veg in very small quantities at a time. Eg, 1 small slice of bell pepper each per meal, gradually building up over the week, then test a 2nd veg item, say slices of cucumber in the second week.
But very slowly & take them off of all veg again if bloating reoccurs.
Treat it the same as the first grasstime in the summer, build up slowly.
They should get sufficient vit c from good quality pellets that are in date. Adding the drops to the water can change the taste of the water & make them not want to drink at all.
Good luck & let us know how you get on
Healing vibes & fingers/paws all crossed for a full & speedy recovery
x