I think you can change stuff around the legal definition of marriage and family separately from the tax break part. I'm not an expert, but if you're interested in this sort of thing I recommend "The Whiteness of Wealth": https://www.penguinrandomhouse.com/books/591671/the-whiteness-of-wealth-by-dorothy-a-brown/

From another article about it: https://www.wbur.org/hereandnow/2021/05/17/us-taxes-dorothy-brown

Marriage puts the issue front and center, she says. Most married Americans receive a tax cut, “but there is a significant minority of Americans, when they get married, they pay higher taxes,” she says. “Well, as it turns out, if you look at Census Bureau data, which actually does provide this information by race, you see white married couples are more likely to contribute income … that leads to them getting a tax cut.”

However, Black married couples are more likely to contribute income to the household in a way that leads to higher taxes, Brown says.

For example, “let's say someone makes $50,000. As a single person, their taxes are going to be a certain rate,” she says. “But as a married person with a single wage earner, that $50,000 household is going to wind up paying less taxes than that single wage earner had they remained single.”

Census Bureau data shows single wage-earning families are more likely to be white than Black, she says. For example, many of these types of single wage-earning families consist of a working white man — a person who statistically holds a higher paying job than any other identity, she says — and a woman who stays home with the children.

“On the other hand, the couple where both spouses are working full time and contributing roughly equal amounts to household income, they don't get a tax cut,” she says. “That couple is more likely to be Black than white.

So. When you running for president? you've got my vote lmao