Officers were searching for John and Donna Broadway after Wilf Isaacs, 50, died at Chubbards Cross caravan site.
Donna Broadway, 26, was arrested on suspicion of assisting an offender after handing herself in on Saturday.
Seven people are being held on suspicion of offences including murder and attempted murder.
John Broadway also handed himself in on Saturday, in Lichfield, Staffordshire.
The other suspects arrested are:
Police believe a shotgun may have been used in the shooting, and are searching for the weapon.
Police investigating the suspected murder of a man who was shot at a Somerset caravan park have made a seventh arrest.