Hi, Ved.
It's not completely clear what protocol your app(s) will use at the moment. As your use term "Serivice Provider", I guess it will be SAML, correct?
1. In general, this could be achieved by simply using several custom authentication scripts at once. They may have a similar logic, and simply will use different login page. Apps using OpenID Connect can select specific auth script by providing its name in `acr_values=` url query parameter. But in case of SAML it may not be this straightforward. So please provide more details of your setup.
Items 2) and 3) contradict to your statement that you will use some different (home-made?) app to register users, if I got you right. Which probably will push new user accounts to Gluu via SCIM. Why do you need Gluu login pages to be involved in registration flow? Could you elaborate a bit on this too?