"DP is in the course of drafting his will to leave his house to his son and his pension to his sister."
It is very telling that he feels no obligation or desire to provide for you financially at all. It's understandable that he should want to leave most of his assets to his son, but not that he should choose his sister over you.
However, I think you are being very naive in your assumptions about the wills and how they should be drawn up. If a couple is married and has children together (none from previous relationships) it makes sense to leave money to each other and then children. But you're not married and you each have a child from previous relationships, which means that legally and morally your first obligation is to your own children and not to each other. He clearly doesn't see you or your DD as part of his family, so don't expect him to pass anything on to her if you leave it to him!
I advise you to leave everything to your DD. Including your house that he lives in. He owns his own property so he could easily give his tenant notice and move back in there. In the meantime he could probably stay with his sister, right?! That's the least she could do given that he's leaving her his pension!
I hope you don't have joint accounts or finances and all the bills and expense are split fairly between you. That is, paid in proportion to earnings/income (eg if one partner earns twice as much as the other, they pay twice as much towards bills and expenses).
I would also be thinking about other indicators of his attitude and commitment to the relationship and asking myself some searching questions about whether he has failed to show commitment or generosity in other ways.