@Ios ****************
The requirements for the extension of stay based on visiting Thai family depends on your local immigration office. They generally require:
1. Your passport, and a copy of:
a. Your data ("picture") page
b. Your visa
c. Your entry stamp
d. Your departure card
2. Your wife's Thai ID, and a back and front copy of her ID
3. Your marriage certificate, and a front and back copy of your marriage certificate
4. A copy of your wife's housebook (she'll know what it is)
5. Your wife to be there
6. 1,900 THB for the extension of stay fee
However, each immigration office may have their own, unique differences.