So hearing that along with hearing someone see's a description of XH truck in my driveway made me feel he could've been here trying to find evidence Im an unfit mother, with the OW by his side. Im not the best housekeeper but for the love of god we're just talking clutter.
Fix the clutter. Really, for now, I know it's a pain in the neck and not a priority in your life - but knowing that OW is the way she is, I wouldn't give him ANYTHING he could use against you to try to get custody. Just turn into Suzy Homemaker for a while. Get a well-organized friend to come over and help you (while blasting dance music and drinking margaritas )
And as for the kids' weight issues - this obesity epidemic in our kids is scary. Something in our environment and/or food is really really bad. But now is the time for you to help them - get them out doing fun physical activities with you, start making healthy foods at home with NO added corn syrup or sugar. Whole foods cooked at home as much as possible. Cut down on the flour and sugar and corn-based meals, more veggies, meat, and fruit and nuts. My kids (in their 20's now) were at the forefront of this problem and 2 of the 3 suffer from weight problems - in retrospect, I wish we'd had the awareness when they were the ages of your kids, I might have been able to do more (mind you, we mostly ate "healthy" and didn't have sodas or candy or such around - but now I regret every fast food meal and pizza night and Sunday bagels).
So just don't let defensiveness against your ex, blind you to the need to help your kids find better health.