My Requirements are,

a)if user is logged on main site, and goes to forum, they should not be asked to sign in.

b)if user has saved a url OR goes directly to forum without being logged in on main site, they should be redirected to main site login page.

c)Any user: password change/forgot password etc links should be disabled.

d)On creation /changes on main site of user account, user password etc, modify it in UBB database as well
OR
have UBB use main site database for credentials.

are all these possible with UBB forums.