Don't acknowledge the rumors. Address the invitations as always. In fact, it would be rude not to; they are still married couples, and as you are inviting people with their partners, you must invite them.

Absolutely don't add "and guest" under these circumstances! (Do I need to explain why?)

If you are very, very close with them, you could ask about how they would prefer to receive invitations. But if you were close enough to ask about such a sensitive thing, you'd know whether or not they really are divorcing anyway.

I recall that a week before our daughter's bat mitzvah, we heard that one couple was divorcing (more than a rumor; we knew for sure). We wondered if we should change the table assignments for the party. We ultimately decided that if it would be a problem, one or both of them would call with last-minute regrets, or they'd call and explain and ask to be seated separately. Anyway, they could just sit separately at the table (seats weren't assigned, just tables). IIRC, they came together and sat together and it all worked out just fine. In fact, I was impressed at their maturity in not letting their own circumstances make anyone else uncomfortable. I wouldn't have thought less of them for declining, even last-minute, in this case.

In your situation, the employees can easily attend without their soon-to-be-ex-spouses if they prefer.

That makes sense. It could certainly cause hard feelings if they would reconcile.
Thanks!