Ideas are very cheap - worthless actually, if you can't execute them into a product, let alone a product that users will actually pay for.
I don't know your current salary, but it should be a hell of a lot more than $100k in SF. So yes, 2% is low, especially given that it doesn't sound like there is an MVP or demo product existing - i.e. you would be building this as your role. Whether they like it or not, you're technically a cofounder, however as you're receiving some salary, you're not taking anywhere near as much risk and shouldn't receive as much equity as them - assuming they're not paying themselves.