With the children, all you can do is protect them, and comfort them. Your wife is still their mother.
Your D 14 is...14. Your wife is doing damage to their relationship, hers and your D's. Not damaging your relationship with your D.
You have told your wife that you do not like this. There is little else you can do. You have told your D, let your mom know. Which is good. Was it one sided?
I told my boys, "If either me or mom are doing something you don't like, let us know. Talk to us. It is a confusing time right now for me and mom. Now, just to let you know, I'm not talking about changing your bedtime to an hour later or anything like that. But if you think we aren't spending enough time with you, stuff like that."
It is in your best interest to keep life as fair as possible for them. They will remember it.
I think you are doing well in regards with your children, but it is worth repeating.
DO NOT influence your children with how you feel about the OM, or what you might think is wrong with your Wife.
They will remember and it will shape them much more than you think it will.
Experience is a brutal teacher, but you learn. My God, do you learn. - C.S. Lewis
Life is usually all about how you handle Plan B. - Jack3Beans
Listen without defending; Speak without offending - FaithinAK