Like previously posted, totally separate companies. NJA is a unionized pilot group with standardized work rules, pay scales, etc. All generally seniority based on upgrades and equipment openings, schedules, etc. 91, 91K, and 135 flying.
EJM, however, is totally separate and different. Pilots are interviewed and selected by the individual owner of the aircraft (with EJM assistance). Pay, QOL, etc is totally based on the individual aircraft's owner. 91 and 135 flying. If EJM loses the management contract of the aircraft, there goes the pilots job. Of course you may interview for another managed aircraft, if a seat or opening becomes available. No guarantee. Also, if you are SIC on a Excel in California, and the owner of another Excel in Maine is looking for a PIC, again, no guarantee of interview, and the Maine Excel is under no obligation to do so. You are not entitled to the seat at all just because you work for another EJM managed aircraft. You may have been an SIC on the California Excel for years, and the Maine Excel (again if separate owners) has no obligation to hire or interview you for their Excel. They can hire whomever they want (if qualified of course).