Private ceremony?

No, it's not okay. Unless your ceremony is your immediate family only (parents and siblings) this is considered very rude. Either invite 70 guests to both ceremony and reception, or do immediate family only.

Https://allwording.com/wedding-reception-invitation-wording/

Despite the previous conclusion jumping, it is fine as long as those 20 people are immediate family on both sides. None of us has any idea how big your families are.

Nope. IMO, 20 is not private. Unless this 20 is only your immediate families (parents and siblings) but (and this is just me) if my immediate family is that large, the ceremony isn't really going to be that intimate, and you may as well invite everyone to both. I think the other way to do this would be to elope with your 20 people and then have a celebration of marriage when you return.

ETA: clarity.

It's okay to have a private ceremony and invite more guests to the reception. Make sure you are not playing favorites with your guestlist and are truly keeping it private. 20 people seems a little on the large side, but some people do have large families.

The reverse is not okay because the reception is considered a thank you to guests who celebrate with you.

It's ok if it's immediate family only at the ceremony. People's feelings get hurt when you start cherry picking.

ETA: Mine and DH's immediate family is 15. I could see someone having 20.

That's exactly what we are doing, but the people at the ceremony are strictly immediate family - grandparents, parents and siblings. The reception (no dance, just food and drinks) afterwards will be bigger with extended family (aunts/uncles/cousins) to help us celebrate. So both are family only, but the ceremony itself will be private with just our immediate family.

No

So sorry, should have clarified. The 20 ppl would be our bridal party (of course) and immediate family only. The other 50 would be extended family and friends.

Not if it's the same day, no. It's completely different if you get married and have a reception (or party) a week or so later.

Bridal party is mixture of family and close friends

Honestly, I looked at doing the same thing bc my FMIL wants this huge wedding and I always wanted something more intimate. However, I would want my 2 best friends there and FH would want his. I was afraid people would be really offended, and I thought about it further and realized I would be too.

A lot of people say it's rude but I say good riddance to that. People get butthurt way too easy. Back up and remember this day is about the bride and groom, not aunts, uncles and cousins you rarely speak to. We are having a small ceremony on the beach, immediate family and our attendants (BM and MOH only). Then we are planning on having a very casual "reception" after for his extended family and local friends. We are going to do the same a few months later with my extended family and friends in Colorado. They don't have to bring gifts if they don't want to, we just want to celebrate with them. And if they want to be offended by that, then they can just not come.

The OP has clarified that it is wedding party and immediate family. In that case, there is no breach of etiquette.

My brother had to do that at the last minute - his planned outdoor wedding ran afoul of a hurricane and we had to put it together on my parents' indoor porch. We could only fit 10 people! The reception went on as planned on another venue.

I think some non-immediate family members were upset that they couldn't attend the ceremony but there was literally no room, and you can't argue with a hurricane. Overall people seemed perfectly happy just to attend the reception and celebrate the marriage even though they hadn't personally witnessed it.

Nope

You do you boo

Yes, it’s fine. My first wedding was siblings parents and grandparents only followed by a big reception. It’s not like inviting people to the ceremony but not wanting to pay for them to be wined and dined at the reception, which would be extremely poor etiquette.

This is not a 'tiered' wedding, and it can certainly be done IF, and it's a giant IF, the only people invited to the ceremony are your parents, GP's if you're lucky enough to have them, siblings and their SO's.

It's fine. We do it all the time.

And it's not a "you do you" quite possibly the worst string of words ever used to justify rude behavior....)

If her BP is friends... how is this proper etiquette???

From WW, i learned that this works ONLY if it's Parents, siblings and GPs... Not including WP that's friends..

Celia, I have to agree. I can't stand that phrase. "You do you boo"... no just no.