So, I have treated all 3 carboys with powdered skim milk for 2 and a half days. Prior to that I had cranked the free SO2; which had already improved things significantly. After that I racked them all into clean carboys. Among the 3, I would say that one was further improved a bit by the milk treatment , and the other two did not improve further in a noticeable manner. The treatment did not hurt anything at least, but obviously took time.
Only one showed signs of some clumping of very small milk curds that I could see. the one that had a high Ph rise came back down, which I expect was also due to the fact that the portion I had tested was the wine most exposed to the air at the neck of the carboy.
all in all, I could have probably solved the issue with additions of fso2 without the skim milk treatment, but it did not hurt. At the end, I am glad my wines no longer show objectionable signs of oxydation as far as I know. 2 of them are still a bit « fizzy » but the fizziness goes away after waiting 10-15 minutes before tasting, and the taste is along the lines of what I would expect. I have noticed this in commercial wines as well.
Disaster averted!
Cheers