Choc, If she is not strong enough to get the kids in line (and boy do I agree that they should be pulling at least 50% of the workload around there), then can you step in and help with that?
Perhaps a chart listing what each kid is responsible for on a daily basis and with the idea that if it is not done, they are grounded from whatever they wanted to do that day. Dad is the one who will be checking things over every night and giving his approval or punishment.
In other words, if this is not her strong point then it is pointless to have that task assigned to her. She will continue to feel overwhelmed and will continue to not handle it properly.
Having said that, there are a LOT of women who really relish this martyr role. I have a sister as well as two sisters in law that do this. I have never understood it. I do believe that it is their way of carving out their 'niche' in life...they are needed because nothing gets done without them.
My BIL did something unusual with his wife. He basically told her, Take one evening per week to go and recharge yourself. You can do whatever you want during this time.
The stipulation is that this should cut down on her complaining time. She sometimes uses this time to grocery shop, etc, but he has told her "hey that is your decision, you won't get any sympathy from me if you use your time to do household stuff." So he fights her complaints with action.
I know many women will say that they just want empathy and someone to listen and validate them (I do too) but there comes a time when enough is enough. If validation is allowing that person to stay stuck and not take responsibility for their own happiness in life, then they may need a kick in the pants to get outta that rut.
Just some thoughts and good luck, Chocolate. I personally cannot stand whining unless there is a REALLY good reason for it (such as being nine months pregnant, LOLOL! See how I always ok it for myself...typical woman, eh!).