Hedonistic Megalomaniac

I do think they fucked Bella together. That's not debatable to me, it's my pet headcanon because to me there is a lot of tension between Rodolphus and Voldemort that would eventually need to go somewhere. Also, the two fucking Bella at the same time is hot and that woman deserves nice things in life.

If you're asking about them alone, then maybe? But I don't think so. At least, not without Bella around, but who knows what those two did when she fell asleep and they were still hard.

I think they mainly had MfM threesomes because Bella was the center of the attention (she loved it), so Rod and Voldemort didn't have that much interaction, and both were Tops and Doms mostly. However...

I hc Bella would be really into double penetration, but even more into double vaginal penetration, so that means their dicks would be touching inside her. The positions for this usually require the two men to physically touch more, so that could have increased Rod and Voldemort's sexual tension a bit. I also think a lot of frotting took place during those threesomes with Bella doing the rubbing.

I couldn't picture them kissing at first, though. But triple kissing gets really messy sometimes. That I'm sure Bella was into that because, again, both at the same time. I think maybe Bella would find it hot if she knew they were only kissing for her, and they also could use this to torture Bella if she misbehaved.

So, I wouldn't discard the possibility of Mfm threesomes with Voldemort always as the Top Dom. I headcanon Rod as a Dom/sub switch for Bella, but they only do that when they have angry sex for real... which happens more often that I thought.