Hi,
I am running new branch lines to another part of the house.
They will pass vertically through a hallway, then on to new area (in walls)
Can I protect four 12-2 branch lines in 1 large pvc conduit.

Thanks

You can but it would be silly.

If you have to fish the wall, you do not have to place the conductors into conduit.

If you choose to place the conductors into conduit, then you need to be aware of Table 310.15(B) (2)(a) so that you can adjust the amperage because of heat.