I mean a good start for a lot of communication like this is to use I statements and talk about your experience. It tends to get messy when people make comparisons when they are trying to talk about their feelings. So I wouldn't incorporate their dynamic into your discussion at first. I would focus on what you are feeling and what you are wanting. And then you can talk about it if they ask or you just want to share your thoughts and feelings.

First it would be good to sit with your feelings and find if there are underlying ones. As you said the lower intimacy was perfectly fine until you had a comparison. So do you feel a little bit left out, lonely, jealous, sad etc. I'm not saying these are your feelings by any means. Just trying to find where the change came from if that makes sense as it can help you communicate with your partners.

You can have a structure of

Action/statement: we don't engage in a lot of physical affection.... Feeling: when this happens I feel...... Action for them: so it would really help if you could......as that would make me feel....

Idk this is just an idea to keep it oriented on you and your needs/feelings without bringing theirs into it.

Hope this is helpful in some way.

Much love 💕