I agree. Under the old 310.15(B)(7) table a few cycles back it was much more ambiguous what the actual 'ampacity' of the conductors was. But the way 310.12 is worded nowadays makes it as Don says.
You cannot use the 83% rule on the feeders because neither feeder by itself supplies the whole dwelling and they are smaller than the service conductors. That's the end of that discussion, taps or not.
Now you also have taps. They can't use the next size up rule so with 4/0 Al they can't be on more than a 175A breaker.
If, say, you instead had a 400A distribution panel with a main breaker and two 200A breakers, 4/0 Al would be okay if the calculated loads were 180A or less.
OP Here are we agreeing that this post is correct? And also that SER Cable cannot be run through the wall and attic (tap conductors need a raceway)