In-laws can cause marital problems. 

Some parent-in-laws expect their family to keep the same parameters after the marriage of a child. 
To mother-in-laws, I would say, a husband takes a lot of time, and his family has traditions too. 
To father-in-laws, I would say, not every male is a _ _ _ _ _ _ _ _’s fan. 

Many spouses and in-laws expect the new mate to accept all the rules of his or her family. 
This is not wise, and family rules and traditions should be a part pre-marital counseling. 
To new brides, I would say, his mama’s house ain’t your mama’s house. Pick up after yourself. 
To new husbands, I would say, her daddy’s car and tools ain’t your daddy’s car and tools. Ask, and ask carefully.
Some new mates expect the same latitude from the in-laws that they get from their own family. This is not guaranteed.

Family traditions will be disrupted, and holidays too.

Volunteering your spouse. 
This is a sin. It implies ownership. Don’t volunteer your mate to do something for your family without your spouse's permission. 
If family asks, tell them you will ask your spouse first. If they can’t understand that… Who should you prefer? 

Some newlyweds often expect their mates to love their family the way they do. That’s not guaranteed, and I'm not sure that it's possible.

People resent being told who they’re supposed to love, and how much. 
One man’s free-spirited 4 year-old niece can be a complete brat to his new wife, etc. 
One woman’s sweet dad can be a complete ogre to her new husband; someone he never wants to spend any time with, or leave the kids with. 
The sibling that is always mooching gas money will probably cause marital stress. 

Knowledge is power and peace. 

Likewise, the newlywed should not expect the biological family to be immediate thrilled with their choice of a mate. 
No matter how humble or dysfunctional the family, every son-in-law or daughter-in-law has to earn their way into the hearts of in-laws.
And this is not unreasonable.

Eric J. Rose