Thank you Laura for your comments!

It is not clearly stated in Job 1:4 whether their feasts were held on their birthdays. Some English Bible versions like the NIV and WEB assumed it specifically. Others like the NRSV (New Revised Standard version) and NET (New English Translation) say they took turns in hosting the feast in each other's houses where they would eat and drink.

https://www.biblegateway.com/verse/en/Job%201:4

The practice of familial gathering was evident in Job's and Abraham's time and encouraged by the word of God even today especially in Middle East cultures.

How the sons of Jacob did it clearly worried Job as verse 5 indicates.