I've only had to witness the after effects of one parent telling the kids the other doesn't want to see them anymore and doesn't love them and then keeping the kids away for a month. That should be an obvious no-no.
Other than that try not to talk badly of the other parent to the kids, supporting the other parent's position when the kids are over there and avoiding the temptation to "rescue" them when they call, keeping each other up on what's going on with the kids. They love both of you and shouldn't have to choose sides. They will also quickly figure out what they can get away with at which house, thus the communication need. The hardest part might be letting them talk about what's going on at the other house, especially after more people enter the mix, but it's part of the deal and part of keeping communication open with your kids.
All in all, how they handle it depends on their personalities and your interactions with each other.
Hope you are doing alright too, best wishes to you and yours.
I used to have an open mind but my brains kept falling out.