Legal marriage before wedding

We are recently engaged and our wedding is on January 2, 2021. We are contemplating getting married prior to this. For various reasons, a few being health insurance, modification of visitation/custody of his children (us living together not married is frowned upon and not helping the case and he currently isn’t allowed to have a “girlfriend” in their presence), and of course Covid. My fear is people being upset or just not showing up to the wedding if we are already legally married a few months prior. We don’t want to do just a “reception”. We want the traditional walk down the aisle and say vows ceremony. We already have the venue rented. Unfortunately keeping it a secret won’t be an option. Once his ex wife finds out (and she will due to us trying to modify his custody) she will tell everyone. And I would prefer to announce it myself rather than her. But I’m not sure how to approach telling everyone, explaining why, and hoping they will still come to our ceremony. And just an FYI, everyone coming would be local, we have no one traveling from out of town that would be spending tons of money to attend. And we are not having a bridal party. And we are paying for everything ourselves.