@CheerBear I totally agree with @Teej - it is wonderful that your LF trusts you enough to open up to you even if it is just a little bit at a time. That not only shows that you are a wonderful mother but your LF is comfortable enough to talk to you about the really hard things. That is a big thing for any kid to do so they not only trust you but must also feel like they will be believed and supported ...and they are big things for kids when they have been holding things in to themselves for some time. I can imagine you are super proud of your LF for having the confidence to open up to you like that but also feeling a lot of anger as well for the other parent - as you have every right to be feeling. You are doing everything possible to provide for a safe and nuturing environment for your little fish and doing an exceptional job at that CB - your LF talking to you as they have is evidence of that 
I hear you about the situation with your parent and how hard it is for you. We need that sense of control over things when so much of our lives have been controlled by others - but this is a very difficult situation and you have to 'go with the flow' - not at all easy when you are juggling kids, volunteering, school stuff and your own daily battles. Again though CB you are doing the best you can and supporting your family in this really difficult time.
It may seem at the moment like there is no 'happy face' that you can put on but from an outside point of view you are doing an amzing job in the most difficult of circumstances - and that is not only commendable but shows your immense strength. Reach out to your supports as much as you need to help you navigate all this and know we not only see how difficult this all is but also believe in you - because you really are doing an amazing job CB 