You are talking “nice to have”, not requirements. And siblings may not have a father on their birth certificate, or they may have the wrong man listed.
Point is, I can make any legal contract I want, just as useful as a marriage license, without a state mandate or license.
Write up a contract and get married in the church. Since I don’t recognize the state’s definition of marriage, I don’t have to pay the tax penalties associated with it.
They’re “nice to have” all the way up until things go bad then you find out they were requirements.
The point is from the state perspective a marriage IS a legal contract. So if you go that route the best you accomplished was to spend a lot of time on paperwork to get something that works just like a marriage license.
And then when you die your wife gets nothing because you didn’t write the contract right. Or if you DID write the contract right the state will say “hey you’re actually married give us our money”.