OP - sick children are draining in a way no one understands.
Like you I was the family rock - my kid was serious sick, my parent was dying my siblings stuck their heads in the sand, DH had an affair - his OW pretended to be pregnant to get him to move out, my sister got serous sick, her kid came to live wit us, I was doing chemo days, radio days, working - being bullied at work, stroppy upset teenager about her mum, sick child getting sicker..........
I booked 4 days away with sick DC, other DC and niece - told my siblings and about to be EX that they needed to do the hospital stuff and went away. 4 days later came back - same stresses but everyone else shouldered a little of the responsibility - about 20% but I could cope. Told everyone if I did not go away I would snap - I was .......
2017 is right - if you do not ask, then no one does anything because they think you are coping - I was dying inside.
Speak up OP - it can not get worse and I can guarantee even a small improvement, gives you a better perspective.