Just tested it. It's 4 including the capital ship. Its important to note that Home One is the only capital ship allowed for the Chimeara event.
Home One (capital ship), Ghost, Phantom II (the ships you must have) and one other Rebel ship (I used Han's Falcon, then in a separate battle Biggs) is enough to enter tier 7.
Replies
Home One (capital ship), Ghost, Phantom II (the ships you must have) and one other Rebel ship (I used Han's Falcon, then in a separate battle Biggs) is enough to enter tier 7.