62Granny
You say financially they are ok, perhaps suggest to your son that the cleaners come more often, perhaps weekly, if your DiL is depressed the bigger the problem becomes the more it is getting her down, honestly if you haven't had time since February to clean your room think how she feels , I would try and get her on some type of healthy eating plan , slimming world is easy to follow and family friendly, suggest you go with her to start, I took ages to lose weight myself , Yo yo dieting but have eventually lost 9st with them. Educate the children about Healthy eating and how they must put clean clothes everyday and clean undies etc. drip feed it and they will slowly get the message. But don't criticise, encourage and hopefully the message will get through.
I am not sure weight is the place to start....no matter how tactfully. its not up to other people, no matter how loving, to get her onto a healthy eating plan, a slimmers group or anything else...for one thing if she is depressed that will not help at all....yes make sure the kids have clean clothes and are bathed and properly fed on the days you are there but genrtly gently with the drip feed education....you do not want the kids innocently feeding anything back that could be interpreted as critical even though not intended. how is your DiL's general health? There are things other than mental health issues that can cause weight gain.