Hey you feel the way you feel. If you are not comfortable with PDAs when the three of you are together, then you are entitled to those feelings and to having those feelings discussed with the three of you.
Not liking your partner's OSO is a tough one and it can cause friction in the relationships - all of them. I have been there and I don't have any advice for you, since you are in the middle of it, rather than at the start.
"Listen, or your tongue will make you deaf." - Native American Proverb