Ok if these were mine first thing I would do is quarantine. Which you have done:). I'm pretty sure you've got some bugs:(. Then I would, now you're not gonna like this, but separate and de-pot. Do some investigating to every cactus from the top to the roots. Who knows how long they've been in those planters? Rinse them off and clean them up. Some you may want to throw away because they're dead or close to it. I think you may have mealybugs. To get rid of them you can use a q-tip and rubbing alcohol and rub them off with the alcohol drenched q-tip. You could also use a spray bottle with rubbing alcohol and water. I've heard some people spraying just pure rubbing alcohol, but I don't think that's necessary. I would mix a little h2o to dilute. Oh ya before you do this Google what scale and mealybugs look like so you know what to look for.

Now that you've cleaned and killed the bugs your plants will most likely be wet. So you need to let them dry in a cool shady place for a few days. They will be fine. If you have a garage this is a perfect place for you cactus. After a few days do another check for bugs. You may have to do the alcohol thing again. You shouldn't have that many bugs if you did a thorough job the first time. I put this pic because this is close to what your cleaned cacti should look like. There's no need to be super gentle. I mean don't manhandle, but don't freak out if you break a few roots;)

Now time to repot:). If you want to reuse the pots you need to bleach every nook and cranny of the pots. I would get some new ones because some cactus have probably outgrown their pots. Just get some cheap terra cotta. Now the soil should be fast draining. If you can find peat less cactus mix that's best. You will also need pumice or perlite to mix into the cactus mix. A ratio of 50/50 should be fine. Plant the cactus higher up in the pot. To avoid getting poked you can use tongs, towels, newspaper, and whatever is around your house:)

Now they're planted I would still keep them away from your other plants. Give them a good check every wk for about a month. Just to make sure those nasty critters are gone! Oh ya you can give them a good watering about a week after potting up. I don't know where you live and where you plan on keeping them so I dont want to tell you when you should water regularly. Goodluck you've got a job ahead of you, but once your cactus are happy they will be beautiful:)

Ps- if you find you have scale I've heard people using windex. I've been lucky enough to not have scale so I'm not the best person to ask on how to get rid of them. Mealybugs are a different story;)