Clarification: According to my information it’s not possible for B to keep his already existing Alpha account. So B can not upgrade but has to create a new account via the link provided by A. And I’m not even sure if A already must be Omega…
250k skill points for B is right.
Buddy invites: Buddy invites and rewards from other players
The post of Elizabeth Norn explains the procedure very thoroughly. And it worked, I can confirm 