My husband won't dare disobey his parents

Before we got married, I spoke with him about dividing our time so we can spend Tet with both our families.

For example, we can spend New Year's Eve with my family, then visit his the next day, and vice versa the following year. My husband agreed with that. However, his father did not agree and even got angry and told him: "if you like that, don't come back to the family."

My father-in-law indeed that my husband was the only child, and if he did not go back home, there was no one else to do so. I found that quite inappropriate. My father-in-law said that even if he had a daughter, he wouldn't ask her to come home for Tet, because Vietnamese tradition dictates that the wife spends the Lunar New Year with the husband's family. I think, essentially, he just favors men over women.

I have a younger brother. My mom agrees that if he gets married, it's a good idea to divide time between two families, so each spouse can share the Tet spirit with their family. My husband told me that it would be easier to convince my father to do so after a few Tets. I'm afraid that the older my father-in-law gets, the more stubborn he will be.

I'm also concerned that my husband is not assertive enough when talking with his parents. I realized that during the last Lunar New Year, when I told him I didn't like visiting all of his relatives' houses and he agreed with me, but then forced his parents when they demanded he do so. He only stuttered and did not share our opinions with his family.

My husband is financially independent, but I find him not assertive enough in communication with his parents. Am I being too difficult? Am I overthinking? Is he this way because he just wants to maintain harmony?

If I want to change him, what should I do to help him become more assertive when he and his parents share different opinions?