@Rivertam
Either she's a member of the family, and family help each other out, or she's not. Why are so many people making excuses for her? Babysitting younger siblings is part of family life.
What a load of guff. 'Babysitting your younger siblings is part of family life' in YOUR world maybe. But in the world of many other parents, they don't take the piss out of their older children and expect them to do the job THEY should be doing, whilst they buggar off to do their own thing.....They are YOUR kids that YOU chose to have, so YOU look after them!
Don't you think your kids (especially daughters!) are going to have enough years of fucking drudgery and babysitting, without you forcing it down her throat at 16 while she is still a kid, at school, doing exams etc, and while she should be enjoying her carefree teen years!?!
Who is paying for that phone of hers? Because if it was me I'd be attaching some caveats to that or withdrawing funding.
Nice. Blackmailing and bullying your own kids into being an unpaid nanny to your other kids. Bet they can't wait to leave home. 
@wisdomofcrowds
Are we really to believe that this is the only job in the entire world that OPs husband is able to do? There is a place in between "works over seas for months at a time" and "sitting home on the dole" and it's called "getting a normal but possibly less fun job like the majority of other parents on the planet". My OH had a job that was incompatible with family life, so he found another one! It took a long time, it meant leaving his dream career, and he had to do some evening courses to vary his skill set, but he made the sacrifice because his responsibility as a parent came first.
I agree. Imagine the uproar if a mother fucked off abroad for months at a time, leaving her husband to look after the kids?