Can my husband and I extend our Thai visas after returning from South Africa on March 6, given our current visa statuses and deadlines?

at MOST offices you can apply for the year extension when you have 30 days or less left on your current entry stamp SO that would be anytime after Feb 22, BUT with that being said if your husbands employer has no issue getting the documentation for the extension you shouldn't have issues applying after you're back on the 6th, that still gives you 16 days to get it done.

Keep in mind it is highly likely that neither of you will get the year extension issued on the spot 😮 I think you BOTH will get a 30 day under consideration stamp (unless your husband's working for a BOI/IEAT company).

I would say EACH of you get a single re-entry permit before you go (so you don't lose the 90 day stamps you have now) and let the employer know when you're comin' back and that you will need the documentation for the extension to be ready after the 6th of Mar. I think you wouldn't have any issue doing it after you're back.