Using Membership with Janrain WuFoo

Ok! This site: https://eikaiwacafe.jp is still in under development but I'm trying to integrate all I need once and test them. I'm using WuFoo Forms for registration and Janrain for log-ins.

For the Membership Plugin to work, I need to disable WordPress Registration. But the integration I did with Janrain and WuFoo is based on this.

Please how do I reconcile this? How do make it possible so that users who choses the packages we offer using WuFoo can log in using Membership?

Hope this make sense.

Thank You!