With the assumption that you are in the US/UK/Canada etc.
This is a no to sticking around, the founders are abusing the team and they will fail unless they quickly change. Leave and get a fair compensation for another position, maybe you leaving with valid reasons will prompt them to realize they need to do better.
I don't generally say it as black and white as that simply because usually there is a lot of grey area, but in this case (based on your statements) even if you have never held a position but have a masters you are so vastly underpaid and undervalued that this is abusive treatment by the founders, pre-seed or not. If they can't afford people, they have to be more creative and forthright with people, right now they are being abusive, unfair and under handed by not having things documented in writing (even in basic English without the legalese). There are many ways they can entice people fairly and everyone takes some risk but also has a large upside potential, 0.1% pre-seed after dilution is essentially worthless even if the company makes it (which we all know the stats are slim). From what you wrote it does not appear they are not doing this properly and so you need to find a place that will.
IMO, regardless of startup size, a salary less then 50% of fair market value should never be tolerated unless you have a significant equity position (that after dilution still gives you a solid exit) and have everything in writing -- even then I'd argue for that low of comp you should be a founder or #1 or #2 employee and it should be in writing on when your salary will change, to what it will be and clear milestones with as little grey as possible.
Let me be clear, it is hard as hell to be a founder and get people on board and to pay them etc, I know I've done it more than a few times and most times without taking outside investments, and as a founder I sometimes took no pay for extended periods while eating/living poorly so I could pay someone else. So I am sensitive to their plight and struggles. However, that doesn't give founders a blank check to be douchebags to other people and promise essentially worthless equity positions with a severely below market salary. And to be clear, don't let them argue that as founders they are taking minimum wage so you should be "happy" to get more (seen that pulled, or where they just try to make you feel guilty), they are the founders with the bulk of the equity they should be the lowest paid early on.
