Finding out you’re not really married

My sister in law and her husband of four years found out two days ago that they are not legally married. To make a long story short, he was previously married and thought the divorce was final when he was marrying my SIL. It turns out that his divorce wasn’t actually finalized until a month after his second wedding. The two of them have been filing taxes as married, have opened accounts, are each other’s beneficiaries, and have a child together. They are equally flabbergasted and crushed. On top of that, they’re looking at tax implications, and my brother in law may be looking at a bigamy charge. The clincher in all of this is that they have both been government employees for the past several years, and nobody caught this before now.

They’re handling stuff the way they need to, but just curious how you would feel if you suddenly learned that you weren’t legally married to your spouse.