Exactly how much of their money did you spend? What value did their money give YOU that you had to use it? If I felt the way you do about these partners, I would not have spent their money or I would have returned their investment from my own funds and said "it's not working out, here's your money plus interest comparable to if you had this in the bank the past year. Sorry, but you just didn't come through on any work and startup ownership is a lot of hard work."
It sounds like you did not have any formal agreement with shares/vesting and the usual contingencies, so you should be in a decent position to return their money but keep your code and walk/start a new project on your own.
Now, on the other hand, if you relied on their money to get where you are today... for example, by purchasing advertising to get traffic which provided the traction you needed to find an audience... then as little sweat equity as they may have, they did contribute something valuable. When you get investors, a lot of them don't want to work much on anything but the high-level strategic stuff (what you called emailing back and forth might be the level of hands-on work they wanted to do at that point in the project since they aren't technical).
I also don't know how you allowed this to go on for so long unchecked? It's kind of hard for them to retroactively fix anything in this situation and I can tell you didn't push on them hard enough as they started slacking because you're now in this situation where they think they have entitlements and equity in something that you mentally wrote them out of already. Honestly, at this point, there is not a lot of great advice to fix this because it's gone on too long and they may (justifiably) be wondering what's the big deal at this point? You didn't give them the boot when they started slacking and you spent some of their money. So I'm glad you're not thinking of ditching them now because it sounds like it's a little late to just say "deal's off, I'm on my own" unless you pay back all their investment $.
Good luck, and hopefully you won't loose any good friends in the process. When I "fired" friends in my first startup, it ended the friendship and after that startup tanked, I don't miss the project but sometimes I miss those friends.