I'm getting ready to hang a 200A load center and also connect up a
100A disconnect.

At thge load center location the two branch circuits are coming out of
the side of the structure which has vinyl siding over wood. one of the
branch circuits is currently connected to the old 100A meter.
on the bottom back of the new load center there are two knockout s for
wires one on each corner.
my two branch circuits are SER4/4/4/2 cable one above the other about
two inches apart, and I'd like to feed them into the load center
through the back so there is no exposed wire.
So the question is what are some approved ways of doing this?

can i knock out the knock out then drill another hole adjacent to it
so i have a figure 8 opening? or make one big round hole? the wires
are about .75" diameter. the spacing is about 2.625 center to center,
and the overall hole diameter would need to be a clear 3.5" Don't they
need to be clamped? (they're already weather sealed.
I want the panel to sit tight up to the mounting surface. the other
question is the SER into the disconnect. for the sake of neatness and
safety I want to lay the incoming and outgoing wires flat against the
side of the box, but the onlt connectors my supply house has are
straight ones. FOr lighter gauge romex there are 90 degree connectors,
but my guy says he is unaware of such a connector for this size wire.