@Jürgen *****
>So i have go still to the immigration for a 60 days extension
IF you want to stay in Thailand longer then September 26, you MUST go to immigration and request for an:
Extension of stay based on visiting Thai family
Each immigration office has their own requirements, however it does not require proof of income, or proof of savings. It will require your wife to be next to you, and the marriage certificate.
Once you get that 60 day extension of stay, you can stay until the middle of November.
IF the borders reopen by the middle of November, bounce on your current visa, and you'll get another 90 day stamp. IF the borders *DO NOT* reopen, then you'll have to leave Thailand and go through the quarantine process when you return.