Your two native Reaper options for moving multiple project markers at the same time are either engaging the ripple editing on all tracks and then moving items (markers will follow)
or
encapsulating the markers within a region which you then move (all items within the region will also follow).
Neither of these options is good for simply just moving markers around, so I'm afraid you'll have to get some scripts to be able to do that. Check following topic which has links to scripts by planetnine and heda;
How do you copy/paste markers?
https://forum.cockos.com/showthread.php?t=178250