Alwadaei’s mother-in-law, brother-in-law and cousin were all jailed for planting "fake bombs” and sentenced to three years in prison.
Last month, the activist’s brother-in-law, Sayed Nazar al-Wadaei, had his prison term extended by an additional three years, bringing his total sentence to six years.
During Wednesday’s hearings, his mother-in-law Hajar Mansoor Hassan and cousin Mahmood Marzooq Mansoor had their previous sentences upheld.
Rights groups maintain that the verdicts are retaliation for Alwadaei’s outspoken criticism of Manama’s abusive policies.
The judicial process, which was marred violations also ignored allegations of torture and coerced confessions.
Earlier in December, Alwadaei tweeted that the proceedings were little more than "revenge” for his activism in the UK.