I'm getting married on the 22nd of August, I sent the invites out a few weeks ago. I don't speak to my parents alone anymore as they're alcoholics and were incredibly toxic growing up, but I do occasionally visit their house because my older sister Ava (who basically raised me) still lives with them, as well as her 15 year old daughter who I will just call V.
I invited both Ava and V to my wedding, but not my parents. On their invitations, I said they could each bring a plus-one if desired. Ava RSVPed and said V would attend with her girlfriend. Ava has known V's girlfriend for several years before they started dating, and has always been supportive. I've also known her girlfriend, and she's a very sweet girl and V is very happy with her. My parents don't know about her girlfriend and V has said in the past she doesn't plan on telling them. They aren't necessarily homophobic, but they're quite skeptical.
After seeing Ava and V get invited, my parents tried to ring me (while I was working, so it went straight to voicemail.) They left a message wondering why they weren't invited, which I didn't respond to simply because I didn't know what to say.
The argument started when I went over to the house to see Ava and V yesterday. My parents came home early from the pub, were surprised to see me, and started chatting excitedly about the wedding (as if they were invited.) They then told me about a "plan" they worked out together where one of them goes as Ava's plus-one, and the other goes as V's. I thought the idea was ridiculous, and they should really take the hint that they're not invited. They saw the look on our faces and asked what the problem was, since neither of them had plus-ones. Ava asked them (seriously) how they would know that, but they assumed she was joking. Eventually V said she was bringing her girlfriend (my parents know her by name but they think she's just a friend.) They called V disrespectful and said she shouldn't put her friends ahead of her grandparents. Soon after they went upstairs because they were drunk and tired, so I hoped they'd forget about the argument by the morning. Which they did, but they still sent me a voicemail repeating their "plan" and Lord knows how they're nagging at V and Ava (Neither have messaged me yet).