I really want to get my own apartment but I can’t go full time. Any suggestions ?

Since it sounds like your relationship to your daughters' mother is not necessarily a good one and possibly involves mistakes from a time of different choices, what does it matter if she gets bitter over you becoming independent from your mom. You need to be independent and your daughters need a strong father figure, something that isn't available if their dad is barely getting by and needs to live with his parents. 

In regards to your career, do what you feel is best. Just know that since children are already in the picture, it will never be easy. In the long run, the more promising path will be the one that rewards you and your children. You may end up being the rich parent who offers a better life, but never let this be your motivation because that mindset will seep into your children's innocence and give them the wrong message that may make them resent their mom for not having more money like daddy does. 

You have children already, so your life will never be easy. Keep your children in mind and do what you feel will help them be able to succeed in life. Be the strong father figure they need. 

just get your own apt anyways

Not sure what the question is.  I worked full time  48 hours a week and went to school full time at nights to get my BS in Business.  You live with your mother so you should still be able to handle it all.  Remember, it won't be forever, once you get your schooling done you will be in a better position for your daughters.  Your ex is going to have to deal with this,