Some of our corydoras have missing whiskers but seem to doing fine. will they regenerate in time?

I’ve owned corydoras catfish in the past, and yes, damaged whiskers do grow back eventually, but it will take awhile, about several months. Just keep the water clean——corydoras catfish need clean water, they don’t like water to get dirty (that is, old water that is high in organic matter or nitrates). Clean, well-oxygenated water will aid in the whiskers’ regeneration. Sometimes, old or dirty water causes the whiskers to degenerate. Do regular weekly water changes.
Also, make sure you have gravel that is not too rough or sharp that may damage catfish whiskers. Rough substrate can hurt healthy whiskers. It is better to have smooth substrate, like some of the rounder pebbly gravel that they sell in pet stores, or smooth sand. And watch other fish that you put in with corydoras catfish——aggressive or nippy tankmates can pick at a corydoras’s whiskers and damage them.

Here is some extra information I found on the subject. I hope this helps. ;)

http://www.fishlore.com/fishforum/corydoras/63046-cory-barbell-loss.html

@MRSHINYSHOES Thanks for that. The tank mates are neon tetras and there is one betta but he seems to keep to himself. I have 4 corys and that should keep them strong as long as they all hang together. there is the bubble wand at the back so plenty of O2. We’ve had them for 2 weeks so I guess they got nothing but time to fill out.