I fall under the "anyone else" category - hope it's ok if I respond....
Different people have different styles of communication, and I think that this can complicate things.
I think there are some pre-requisites for having an easy time communicating difficult stuff.
The first is trust - this allows the parties to look at the real issues, rather than trying to second-guess what may be underlying what is being said.
The second is mutual understanding of the communication styles. Will speak more to that below.
The third is environment - it's important to have a good time and place to have the discussion.
When you get into the discussion it's important to frame what you are going to say - if it's a minor thing, say that, if it's something major, say that too. What you don't want is for there to be surprises half way through because that will tend to hijack your listeners' trains of thought. "You said that you had a problem with quality time with your partner, whereas what you are really saying is that you have a problem with me going out with your them!" Also, frame what your desired outcome is - example "I would like us to talk about this, give everyone a chance to talk about how they feel, and then try to come up with a solution that we can all live with."
Try to phrase issues in a way that encourages the team to work together at a solution, rather than blaming someone and making it an "us against them" proposition. When you are in a poly relationship, most problems end up being shared problems - solutions are found easier when everyone feels part of the team (this isn't always possible in every circumstance, of course).
OK, communication styles - I am going to be horribly general here, because there are many shades, but... extroverts have a tendency to want to talk through their thought processes. This means that they like to sit down with their trusted loved-ones with only half-formed thoughts, bouncing ideas off them and getting feedback to reach clarity in their own minds and be (hopefully) half way towards a solution.
The danger with this is that sometimes the train of thought (and therefore speech) can be full of some pretty scary things for the listeners to hear and that can be counter-productive. Also, if your listeners are introverts, it's going to seem like you are babbling. If you tend to be an extrovert and your partners are introverts, try to do your best to sort out some stuff before you talk - even if it's to come up with some bullets. (By the way, this feels very uncomfortable, because it goes against the grain of your natural way of thinking).
On the flipside, if you are an introvert, then you tend to not want to talk until you have everything worked out. It's only then do you want to sit down with your loved ones and present this. One of the problems with this is that your listeners sense that you alreayd have it worked out, possibly with a solution that they aren't a part of, and it's a case of just accepting whatever is said, or rejecting. Another issue is that because you have waited so long to talk about the issue, it may well have got a lot worse in the process, and therefore be much more difficult to find a solution. If your partners are extroverts, try to encourage yourself to talk without having everything worked out in your mind, and trust your partners to work with you - you don't have to have all the answers before you talk with them. (By the way, this feels very uncomfortable, because it goes against the grain of your natural way of thinking.)
This is in no way a value judgement on the extrovert/introvert scale, merely observations of the different communication styles that tend to feel natural to each extreme. Most people are in a grey area, but tend towards one or the other.
Once you get into the discussion, make your you listen as well as you talk. Encourage the other people to paraphrase back to you what you have told them, to make sure that you know that they have understood what you said.
OK, this is long enough already - hope some of this is useful.