“MiaNOT” series (2019) was CaptainSparklez+TheSyndicateProject(Tom). They did talk with each other in that series, but not as much as I like.  
“How To Minecraft” (2019) series had CaptainSparklez+IIJERiiCHOII(Tucker). Very briefly talked at the start, never talked again.  
CaptainSparklez+OMGitsfirefoxx(Sonja) did not happen at all, at least in context of Minecraft. He was a guest at her “IDK I JUST PUT MY FRIENDS IN MY TUB” series (2018), and that’s it.
 
P.S. He did mention that some “M-like stuff” was happening in “SMP Earth” (2020) series (not the crew, but like lore and plot).

@Background Pony #6F0E  
I think I saw Syndicateproject had a few videos with CaptainSparklez, though I never watched any of them.

@Mike  
Numerous famous youtubers forming a fully functioning society in minecraft over the course of 200+ episodes. 2-6 hours of livestreaming daily.

What the hell is Mianite?

you should be watching ponies anyway, downvoted