I completed my stay in Thailand with 3 60 day covid  extensions on my O visa. Finally received my 1 year retirement  extension. My 90 day report is due now. ?... do I also have to file my first tm7?  My hotel filed thru September. I moved into my sons mothers house then? Is she supposed to file the TM7? If not ..penalties etc.?

It is a TM47 and you need to do the first one in person at immigration.  TM7 is for an extension of stay.   Your hotel most likely filed the TM30 report of address, you will need your sons mother to do one as well since you moved (requirement is withing 24 hours of moving).   There are penalties for not doing either the TM47 or the TM30, the biggest risk is that it may complicate future extension requests at IO.

Of course, if you're using an agent, nothing is required as I did during my past 2-years stay (20/21). No money, no TM 30. Nothing. I reported 90-day only. 

TM7 is the form used for applying for an extension.

You probably mean TM30. Yes, your sons mother should file a TM30 for you. Has to be done within 24 hours, but she can just put today's date on the form, then there is no fine, they don't know when you actually moved in.