The who moved in with her ex-husband and his new wife for the sake of their kids just welcomed another new roommate: her boyfriend

"For the sake of the kids" - sure. In one of the photos, the new missus looks strained (and no wonder) . Ex-wifey is (1) showing off to hubby that "yeah well I got a new, younger, fitter guy to replace you so sucks to be you" and (2) reminding him of what he's missing (that being 'crazy b-word' is my immediate impression but never mind).

If new wifey wants the marriage to have any chance, she'd better make hubby boot ex-wife and new boyfriend out, because the kids are going to be pawns in all this ('well Mom said I could, and she's my real mom and you're not!') and hubster is going to have all the 'remember when we had the good times?' constantly in his face.

Though I would laugh if new wifey and new boyfriend ended up running off together and leaving the exes with the three hyper kids, which I could see happening (and maybe that's even the outcome crazy ex-wife is aiming for?)

"Mathis added that TK is less involved with parenting logistics and typically goes to the gym after work."

Yeah. She's not letting him be step-dad, he's only there to remind hubby that she's still desirable so look what you're missing out on. Soon as she gets her way, she's dumping him.