As a totally biased recommendation (I'm part of the team there), have a look at Ideaflip. It's basically a shared online board with sticky notes and few other elements like dots, tags and stickers - the simplicity sounds ideal for your use case? It's pretty easy to build whatever workflow you want, and you could have everyone drop in sticky notes with the topics they want to bring up, and then use the dots to do the dot voting. Let me know if it works for you!
I like to try to frame it as 'the team against the problem', not a conflict between team members. When the problem is something like a breakdown of communication between two people, or a clash of personalities, it's trickier. But you can still frame the problem as the dynamic between the people (i.e. external to them), rather than any person being a problem. Then make sure that everyone involved are now in conflict with the problem, which is actually your process or the dynamic that exists between people, not anybody personally.
(This is also the right way to approach conflicts in personal relationships in my experience. It's 'us vs the problem', not 'me vs you')
To quote what I wrote in a [recent blog post](https://ideaflip.com/blog/3/retrospectives/):
> A retrospective is not an opportunity to moan and complain about your teammates, or things you don’t enjoy. It’s a constructive, mutual feedback session, and the tone of the meeting needs to reflect this. Focus on more than just the negative aspects of your process, and also highlight and praise the things that are working well.
> Retrospectives are not about finding fault with people, they are about improving your process. Problems should be framed as the team against the problem, not teammates against each other. If you’re struggling to work with someone else, focus on the process around this, not the person themselves.