Actually we really not recommend you to use multiple Membership System on a single website. Because it will causes some conflicts and will have bad impact to you website performance.
If you want to use another membership system, you can disable Youzify Membership System ( Please check this article >> https://kainelabs.ticksy.com/article/13273/ ). That's mean you will no longer can use Youzify Registration Form, Youzify Login and YouzifyReset Password. But you still can enjoy other Youzifyfeatures. :)