First, get a current copy of the owners POCO bill and see what the POCO demand figures are. The 1 tenants demand cannot exceed the POCO numbers.
What you would do if 50 is included within the 'base' utility fee is deduct 50 from whatever the guys demand reading is on his meter. For two tenants, deduct 25 KW from each. They will complain, but thats about the only way to do it. The ultimate solution is for each tenant to have a POCO meter.
If you are getting involved with the reading of the subs, I strongly suggest that you obtain at least six current POCO bills, obtain the POCO rates, and determine IF there are any laws regarding sub-metering and pricing.
Here in NJ the rates/fees charged to any tenant cannot be greater than the POCO rates. An 'Administrative Fee' is the onlt adder charge that a landlord can charge. There is no definition of the 'Adm. Fee', but reasonable charges for reading and billing processing were OK.
The multiplier is a factory number, based on the ratio of the ct's and the meter electronics. ie: 200 amp CT's with a meter rated at 200 amps, 1 multiplier; The CT's are usually 5 amp output on a 200 amp load; different CT's result in a different multiplier. A '1' is easy!
