It's definitely NOT horrific, horrible, terrible, dreadful or any of the other catastrophising words people have used to over dramatise this unfortunate situation.
But it is, indeed, hurtful. I think anybody would have felt hurt by this.
What can be done about it? Realistically, nothing. `
I would definitely not have let them know, I would have removed myself quietly from their lives and archived the group and if (and that is a big if) they came asking would have told them breezily that as you and your children were not invited to the weekly lunches you had taken the hint.
These people knew they were excluding you on purpose - and yes it was on purpose, of course it was - why would you give them the satisfaction of knowing they had hurt you? Why make it clear how vulnerable you are?
Oh well, it's done now.
Someone in the group does not like you. There is no need to invent or imagine some strange circumstance where humans do not act like humans or there is some deep and meaningful mysterious reason.
Someone in the group does not like you and that's that, mind reading the reasons for it might comfort you but mind reading is almost never acccurate.
Yes, it is hurtful. But you cannot force people to hang out with you, and should never try - and though you say you would not go to the lunches, which is fair enough, what other reason was there for letting them know you know?
An explanation? They chose to hang out without you, so at least one of them does not like you, that is the only possible explanation.
An apology? From your perspective, what possible apology could erase a whole year of deliberate snubs?
From their perspective, why should they apologise for enjoying a social meet up with their family? They won't be apologising, so you should just put your phone down and get on with it.
A happy, fulfilled life is the best revenge. Next time one of them brings it up tell your husband to say, oh she was just so surprised, it wasn't worth mentioning really. Forget it, we have. And make sure you relegate them all to the bottom rung of importance in your life, insofar as you can.
You must find a way to simply interact with them casually at times when it cannot be avoided as they have made their choice. And now that you have had your say, I'm afraid you will have to just let it go and avoid them as much as possible. No more favours, your husband can deal with his family and you can be polite and no more.
Time tends to lend perspective too. In a couple of years, things might be quite different.