Extended family tension is one of the most common sources of strain couples deal with, and one of the least discussed openly, since it can feel disloyal to complain about a partner's family. Left unaddressed, it doesn't stay contained to the in-laws. It tends to leak into the relationship itself.
The conflict is rarely really about the in-laws
A frustrating comment from a parent-in-law or a disagreement over how holidays get split is often standing in for a bigger question: whose family takes priority, and whether your partner will back you when it matters. Addressing only the specific incident tends to leave that underlying question unresolved.
Present a united front, even when you disagree privately
Disagreements about how to handle family are normal and worth having, but they're best had between the two of you, not in front of the family member in question. A visible split between partners in front of extended family tends to make everyone's position worse, including your own.
Whoever's family it is usually needs to take the lead
It's generally easier for the partner who grew up in that family to set boundaries with their own parents or siblings than for the other partner to do it. That doesn't mean the other partner has no say, it means the actual conversation with family usually lands better coming from the person with the existing relationship.
Set boundaries with family, not just with each other
A lot of in-law tension gets managed entirely between partners, without either of them ever actually addressing it with the family member involved. Boundaries that only exist in private conversations between you two don't change the behavior that's causing the friction in the first place.
Revisit the agreement as circumstances change
What worked for holidays or visits a few years ago may not fit anymore, especially after major life changes like having kids or a family member's health declining. Treating the arrangement as a fixed rule rather than something to periodically revisit tends to build resentment on one side or the other.
In-law conflict is rarely solvable by fixing the in-laws. It's usually solvable by the two of you agreeing on where you stand, together, and communicating that clearly to family, even when it's uncomfortable.