After lurking here for quite a while, I'm totally side-eying all of my cousins horrible etiquette for her upcoming wedding.
1) I just actually read the invite as my Mom mentioned RSVPs are due Jan 1 (for an Aug wedding). I don't f'n know what I'm doing a month from now! Never mind in August, that's just crazy to expect confirmed RSVPs over eight months in advance!
2) She started a GoFundMe page to raise money for her wedding, and was posting it all over FB. Wrong on all levels. I think her Dad got wind of it and shut that down right quick, and after about a month she had only raised like $50 so I think most people knew it was bad taste.
3) Her wedding website specifically asks for no gifts and just donations to their Honeyfund... Barf. They went on like a 3 week European vacation just over a year ago that they managed to pay for themselves.
4) I just actually read my invite because they're apparently due, and my FI and partner of 5 years isn't invited at all. I wasn't even given a +1. It specifically says: "Please RSVP by January 1st 2016. If your invitation does not mention a plus one, then we do not have room at the venue for any additional guests. Thank you for understanding." It's not even like my FI is some random she has never met. She has not only met him but she has spent the night in our home, that we have owned together for years! I am just so deeply offended by that. We have been together longer than her and her FH have been (not that that matters at all, but it's not like my FI is new to the picture). I really don't know if I should just decline on principle (he can't actually make it anyways because he works oilfield and is on shift, but still, she doesn't know that!) or if I should ask her to see if she genuinely made a mistake. I don't even know if I care at this point. It's such a gong-show.
And finally 5) Huge gap which leaves me in the middle of a city about 2 hours away from home with no SO and nothing to do.. Because pictures!
Ugh. It's so horrible I just had to share

Re: Offensive Etiquette all over!
That's an easy no. Hell, #4 alone is enough. You don't disrespect my SO or our relationship. I wouldn't even call to clarify - they put it right into invitation that if you don't see it, it's on purpose. It's clear they can't afford their wedding, so consider your gift to them that they have one less person to pay for and decline that mess.
I say skip this wedding. There are much better things you could be doing on a weekend in August!
I cannot imagine anyone able to RSVP 8 months out. As a teacher, I have some decent flexibility, especially in the summer months. But school begins in August, and that calendar does not come out until at least April.
I'm curious about that 8 month window. Is this any type of destination wedding? Is the family so large that she has a B/C/D list? I have declined weddings that have had a large gap. Pair that with excluding my SO and you have a no-go from me!
Why waste your time.
Please don't go to this, but I do hope you update us as much as possible.
Can you RSVP maybe? That's usually an option for an evite. Or RSVP yes now, but feel free to change your mind in July.
I feel like there is probably much more to the story here, but your cousin was not obligated to invite your parents. Adults get their own invitations, which are not contingent on anyone else's invite- thus it is perfectly fine to invite some and not others.
But from your personal situation- this is why it is recommended to invite in circles. And likewise, you are also an adult and are free to decline any invite you wish, for any reason you wish.
ETA clarity.
Screw that. I'd say you already have plans 8 months in advance.
SaveSave
Your cousin sounds as rude as cow manure. I hope that you extend the same kindness to your cousin that they have bestowed upon you and your SO when you all get married.
I get the temptation of going just to see the shitshow unfold, but I really think that just validates what they are doing to them. It's telling the couple that you are ok with your SO not being invited. I'd decline on principle and use CharmedPam's line if anyone else asks you why are you aren't attending.
Decline, decline, decline!
"Love is the one thing we're capable of perceiving that transcends time and space."
Or do what PP said and RSVP yes now, and then conveniently change your mind in July.
First, just ignore it. Don't RSVP. If she starts hounding you for a response, reply "Oh, I thought that was just a Save-the-Date since wedding invitations are expected 6-8 weeks prior to the date at most! Let me get back to you". Then wait at least a week, ideally until she hounds you again for a response. Then reply that "I looked at our calendars, and we'll probably be able to make it". See if she follows up about the "probably" or the "we".
Oh, and for a gift, I would 100% give a gift card for a store. Not cash, and not contribute to the honeyfund. Unless the above goes really poorly, then I'd just give a nice card--no gift.