Kamnuan Chalopatham, the former Sing Buri senator, and former Maha Sarakham senators Prakiat Nasimma and Srimuang Charoensiri are included in the group.
Meanwhile, former MPs who had sided with the Matchima group of Somsak Thepsuthin, decided to return to the PPP, claiming the National Referendum results have shown that people still support Thaksin.
Suchart Lainam-ngoen said he had already told Somsak that he will join the PPP, adding that Somsak had respected his decision.
There was plenty of activity at the PPP headquarters at the IFCT building on Tuesday, as many Northeast members attended the meeting to fill out their application forms and pose for photos.
Northeastern members also picked Songsak Thongsri, a former Buri Ram MP -- and a close aide of Newin Chidchob -- to head the Northeast constituency, which is in charge of selecting candidates to field in the election. Songsri was a member of the anti-coup group called "Thaksin supporter. No coup".
The Thai Peace Party leader Pichate Satirachaval also agreed to join the PPP after he attended the party meeting on Tuesday.
He said he was ready to join if the PPP restored the Southern Border Province Administration Centre (SBPAC) to solve the problems in the southernmost provinces.
Boonjong Wongtrairat, spokesman of the Northeast provinces said most candidates were ready to campaign in the Northeast constituencies. He claimed that some members of the Saman Chan group and the Matchima group "will also join the party."
He said the PPP will call on the government to lift marital law in the 35 provinces.