How to multiplex multiple displays?
The code instantiates two instances of the SevSeg class.  This may or may not work.  Really depends on if the class uses any resources are not meant to be shared between multiple instances of that class.  For instance, it is unlikely that one hardware timer can be used for more than one purpose at a time.

But the code continues on to use the same (anode) pin resources for both instances of the class. This is likely not going to work.

Apologies for being vague using qualifier like "unlikely" instead of simply stating that it will not work.  Truth is, one might be able to write a class that can deal with multiple instances of its self.  But it would be very difficult and a far more complex programming task than to simply use one instance for all 8 digits.

In case there is a question as to the maximum number of digits supported for one instance of the SevSeg class, this line is in the one of the SevSeg header files:

#define MAXNUMDIGITS 8 // Can be increased, but the max number is 2^31