A. YES, it is possible to set it up using our API so that when someone joins the 3rd party system an account is created in the WMT Software.
If this is possible depends on the 3rd party software.
It would need to be modified so that when someone joins it, it calls the WMT API requesting that a new account is created.
A. ~membership~ = Title of the Member's Membership
~password~ = Member's Password
~username~ = Member's Username
~fname~ = Member's First Name
~email~ = Member's Email
~url~ = Member's Redirect URL
~ip~ = Member's IP (5.0+)
~parentusername~ = Parent's Username
~parentphone~ = Parent's Phone
~parentemail~ = Parent's Email
~parentlastname~ = Parent's Last Name
~parentfirstname~ = Parent's First Name
~surl~ = The domain name of the site (DEPRECATED)
~siteurl~ = The domain name of the site (5.0+)
~burl~ = The domain name of the site with /admin added to it (DEPRECATED)
A. A member cannot belong to more than 1 membership. Instead, you can setup so each membership has different content.
Then make the membership that the member upgrades to include all the content from the member's original membership.
You can do this by setting up content groups and attaching them to content.