The idea that you can postpone the gain on selling your home by buying another home within a certain timeframe was written out of the tax law more than 15 years ago.
The current rules are relatively straightforward. You can exclude the gain on your main home if you have owned it at least two years and if you lived in it as your main home for at least two years of the five years before selling. In other words, because you rented home A for more than three years after you moved out, you do not qualify to take the exclusion on home A.
You appear to qualify to exclude the gain on home B.
Even if you had qualified to exclude the gain on both homes, you can only use the exclusion once every two years. And even if you did qualify to exclude the gain on home A, you must still deal with the depreciation and pay depreciation recapture.
A “like kind exchange“ allows you to postpone the gain on business property if, when you sell it, you acquire a similar piece of business property at about the same time. That might have allowed you to defer the gain on home A, but only if you had purchased a new home D to use as a rental property at about the same time that you sold home A. If you want to defer the gain on home A to buy a new rental home D, it may already be too late, and if not, you need to get on the stick and find a property and get an accountant to make sure you qualify.
