So my parents are divorced, my dad later remarried and then divorced again just a year ago. My father is paying for the wedding along with the help of ex wife #2.

My mother has no financial obligations towards the wedding, but is nonetheless helping me plan. Anyways my question is.. how in the world do I word the invitations? I feel that my mother would be upset if I listed my father and my stepmother, but not her. But I don't want to list her (without listing my stepmother) because she isn't hosting the wedding and that would be unfair to ex wife #2 who is helping pay. It's such a weird situation and I don't know how to word these invites. Any help or advice would be greatly appreciated!
NOTE: I still call ex wife #2 my stepmom even though technically she isn't. Sorry if that confused anyone.