Crocodile, Mihawk, Moria, Law and Doflamingo I can all see joining pretty easily with Boa being forced into it.
Crocodile and Sasori or Crocodile and Kakuzu would be the optimal pairing. People that can be fully used by Crocodile’s long term schemes.
Mihawk would be Kisame, Deidara or Itachi imo. Kisame is a given, I think there’d be implicit respect between them. I think Deidara can cozy up to Mihawk similar to Perona tbh.
Moria is definitely a Sasori or Hidan partner.
Law is with Sasori, Deidara or Itachi
Doflamingo is hard to say tbh.
WBU? Who do you think would be open to joining
Crocodile I think would either reject or end up like Orochimaru and try killing his teamate. He just won't get along with anyone really and wouldn't really be okay with not being the leader. I think Moria could be the same, dude was willing to be imprisoned instead of joining Teach, he probably rejected working with/for Kaido as well. Though I guess both would be interested in the tailed beasts still.
I think Law, Mihawk and Doflamingo would all join. Doflamingo despite his ego is still not really like a crocodile imo, he is into working with other people.
Law and Sasori works. both are no nonsense and would just want to do the mission. I don't think he would like Deidara trying to be too friendly, nor would he want to work with Itachi because of the family killing stuff(would probably remind him of Doffy)
Mihawk and Kisame works since both are swordsman, Mihawk and Itachi also works, Mihawk would be interested in him like he is in Luffy and Zoro, though only Kisame would like Mihawk. He instantly is kind of disliked by Nagato for not showing up to meetings and stuff
Doflamingo and Orochimaru works well, both want to be immortal, terrorists, grudge against their home countries, cult leaders etc. Doffy works with Sasori or Itachi too though