My qualifications to give this advice are nil, but...

Given your differences, I'd think the only way the partnership can possibly work is to focus on creating a neutral platform. That would mean giving up on preferential treatment for effective over religious charities (though you might be able to all agree to penalize political orgs). If your platform becomes what you hope it will, presumably it'll be useful to effective charities without the need for subsidies.

I mean, if you can persuade them to see things your way, that's great, but I don't see it happening.