I'll be moving this post from the Sendy forums to the SCLogin forum after I post this, so look for it there.
I want to have two register field in sclogin
I'm not sure what you mean here. If you want to have 2 instances of the SClogin module on one page, that's not an issue. As for registration itself, the SCLogin module just redirects the user to your registration extension -- either Joomla's User Registration component, JomSocial, EasySocial or a few others. If you need to customize the registration process, you'll have to do it in those extensions.
I hope that helps answer your question,