Man to man, that answer isn’t good enough when you are talking about supporting a wife and family and you may not even be able to reasonably afford the size of the family you want by taking this job. If you are talking about cutting things that close month to month, what happens when the inevitable crisis happens? You already say you can’t support the home you own already on the salary enough to keep that single investment in reasonable repair.
Forget about expensive vacations, what about college savings for your kids and your own retirement not to mention maintaining a decent emergency fund for the long term? It sounds like you won’t be able to sustain it. The lack of excess money will destroy your life slowly over time in ways that you never imagined. It will put strain on your marriage in ways that could lead to divorce. Your child or children will notice that you value other people in the abstract (whatever cause it is) rather than them because you are putting them into financial hardship for something you feel strongly about but probably doesn’t mean a whole lot to them especially when they see you stressed out and their mother pissed off much of the time because you find it hard to pay the bills.
I have literally been in all socioeconomic classes in my life and anything less than upper-middle class sucks. My mother did something similar when I was growing up. She was a teacher for very poor and disadvantaged students, one of the most decorated ones in the U.S. However, she wasn’t a very good mother because she devoted her time to everyone but us and she was a horrible provider because she made crap when I was growing up. She eventually made a lot of money writing and speaking based on her experiences in the trenches but that I still resent her for it because it was nothing but pain and suffering on my side for little apparent reason. You don’t want to be so idealistic that you jeopardize your family’s future and wellbeing for some abstract, idealistic cause. I truly believe charity begins at home and you shouldn’t do anything that puts that primary responsibility at risk.
Don’t take the job. It sounds like the idealistic delusions of someone who is young, ambitious and talented but not yet wise. Jobs like this are more for doe-eyed singles or semi-retirees. You missed the window for the former but you can do something similar much later and more responsibly after your family is secure and the kids are out of the house.