Is it possible to extend the second entry for 60 days based on marriage.

My first entry has already been extended for 30 days already.

Yes, bring wife and marriage certificate.

From Police order 138/2557


2.24 In the case of visiting a spouse or children who are of Thai nationality:
Each permission shall be granted for no more than 60 days.

1. Application form.
2. Copy of applicant’s passport.
3. Copy of household registration certificate.
4. Copy of national ID card of the person having Thai nationality.
5. Copy of a marriage certificate or copy of a birth certificate.

You can get a 60 day extension to visit your wife with any type of entry.

Some offices have even done them after the normal 30 day extension for a tourist visa entry.