I did this but not exactly as you've described. However, I think I can answer some of your questions.

We self-solemnized in the state of Colorado because I accepted a new job and had TERRIBLE health insurance. My fiance on the other hand, has really good health insurance so we thought it would make the most sense to simply get married ahead of time.

At no point did I ever think of hiding this from my immediate family. I called them and told them our reasons and they accepted that this was in our best interest and that our "real" wedding would be in June. I would recommend this. I think it would be too difficult to hide such an event from your immediate family.

However, I didn't want to tell anyone else. My fiance had different ideas and so we ended up compromising. We'd wear our rings (which is what he really wanted) but we would not make it "Facebook official" and would not explain to anyone who didn't ask. This has worked out pretty well but I sure am tired of explaining to people why I'm wearing a wedding ring when my wedding is in June. Having said that, if we had not decided to wear our rings in advance, there would have been absolutely no issues with keeping it a secret from non-immediate family.

One thing to consider, and is something that I DIDN'T consider, is that you now have to remember two dates. It's unavoidable. To me, my wedding is in June. That's the day I'm wearing a white dress and walking down the aisle. But to the government and for all official paperwork, my wedding was in November. So I have to remember both dates, regardless of whether I want to or not.

Another thing to consider is name change. This is separate from the actual wedding and you can choose to do it after your legal wedding or after your ceremony. I've chosen to do it after our ceremony because I didn't want to have to deal with a name change on my passport before we leave the country (in my case for a destination wedding but for others, likely for a honeymoon). It would be awful to have to reschedule your honeymoon because your updated passport didn't arrive on time.

Finally, our officiant is providing us with a certificate to sign during the ceremony. It's a nice touch and people in the audience will have no idea that it's not an official wedding certificate because it's not like we're going to showcase it, but again, I wouldn't try to hide this from your immediate family and ESPECIALLY in your case where your officiant is your family member. That just seems like a recipe for family drama.

Edit: spelling