Use Covid as an excuse, "Due to the pandemic we won't be inviting outside guests to the cottage this summer. Thanks respecting our wishes and most importantly our health."  

About the gskids, 12 is a lot! Birthdays, xmas, all the other holidays add up when it comes to 12 grands.  It's understandable if you're budgeting and can't afford to to shower them with gifts.  I know people who do "family" gifts rather than individual ones.  One set of grandparents I knew of made a donation every year to the Arbor Society in the name of their grands. The gkids names were engraved on a little metal tree plaque and the benefits went to bettering the planet for them.  Best gift you can give is to impart your wisdom.  Tell gskids to marry wisely if they must marry and under no circumstances become step parents!  

Did you agree to DH and SD going off (presumably to the cottage) and leaving you behind?  Personally, although my DH once took my 2 SDs on holiday abroad when they were teens, I wouldn't agree to it now - those days are long gone.  

Sounds like your DH will be rewarding their bad behavior for the rest of your lives.

What you described with the SKs no longer having contact after the gifts, parties and vacations stop is exactly why I'm finishing a week with my adult SSs, SDILs, & SGDs in an oceanfront beach house that will have cost us about $13k for the week. My DH understands full well the very little contact with SKs would stop if those things stopped. I've been married to my DH for almost 21 years, and SSs were 4 and 5 when we married.  I wish I had advice, but unfortunately, all I can say is that I know how awful it is all the way around. Unless our DHs are willing to STOP the spending and face the shell of a relationship ending, I don't see any way to stop the madness. I'm sad for both of us.

No advice but thank you for a well typed out post. Easy to read. 

I'll post the link to this blog that was posted about the same time.  The two seem to go hand-in-hand: https://www.steptalk.org/blog/nothanks/ot-extreme-entitlement-or-sociopa...

You're retired and they are looking for handouts. Nice.

Of course your DH denies there is a problem, because he would have to admit he was not a good father.

Of course SD has come out of the woodwork and wanted a free vacation.  You did the right thing staying home.  If your DH was ok with this, consider youself lucky. Some SMs have to walk into the fire to make their DH's happy.

You didn't describe exactly what was bothering you. Is it that your DH is gone? Or that SD has wormed her way back into his life? Or that he denies there is a problem?

Keep staying home and staying disengaged. Let him deal with his adult children. My SDs are middle aged, DH sometimes sees them (after all, they are his kids) and then we go back to our normal lives. 

Do the skids buy presents for you? How about for their father?

At a certain point, multi generational families simply become too large for everyone to buy gifts for everyone else. Even my late FIL, who was enmeshed and Disney to the bone finally had to admit it was all just too much, and we switched to drawing names.

If these ingrates aren't interested in a gift exchange, let them pound sand.

Adult stepkids wanting parties is unfortunately not an unheard of thing. There's a post on my blog about SD expecting a party funded by her dad who was also explicitly uninvited from the same party. On the plus side you're not alone. On the downside, welcome to the dysfunctional insanity of steps

I find that our hospitality is taken for granted, too.  I am not a great hostess but did my bit for yeats, mostly Christmas.  It was quite an ordeal because i was also working full time, getting my degree at night school and still had to shop for 20 people, cook, rent/return Santa suit, clean, etc.  I stopped hosting a few years ago and switched to money gifts.  Guess what?  Did you know hosting Christmas for a big group is a lot of work?  Really?  It has been rotating from one kid to another with each swearing, " Never again!"  Lol.