So- shared electric lines between homes and not updated since the 60s.
Your problem is in that statement probably.
Electric lines can only carry so much 'load'. That load is determined in 'AMPS' and with distance, the 'Amps" load increases on the line. If you pull too many 'AMPS' you will do 1 of 2 things- trip a breaker or fuse, or start a fire.
You see this when people use an extension cord and run space heaters off the cord, the cord can get so hot it starts a fire. In the old days- mobile homes would use like 50 - 60 AMPS each. So maybe that MHP is set up to handle that amount. A window AC unit will draw 15 - 20 AMPS. A dryer uses about 30 amps. A stove uses 30 - 50 AMPS. Water heater uses 25 - 30 AMPS. In a home one uses a 'load calculator' to figure out how many AMSP of appliances you can have on the circuit. If you have too many AMPS- you will trip a circuit breaker, the main breaker or you could heat up the wires to the point the cause a fire.
That is basic info- here is my take as a park owner.
I have had a park with this problem. There was a fire underground, and we had to shut off the power to fix the line. The city told us we had to fix all the power to turn the master meter back on- so we had to pull power to every home in the park and every home got a meter etc.
The cost was about $2,000 per lot. Power got turned on over time to each home, the first about 10 days after the power was shut off, and the last about at the 17 day mark.
OK- so maybe there are options. A power pole in most cases fully hooked up is about $2,000 per home-site. This assumes overhead power and the pole is close enough to a transformer to even get the power there. If there is no way to get power there overhead- the cost goes WAY up. In some cases that cost might go to 3 - 5 thousand per home. As a park owner, depending on space rents etc, that might shut a park down.
When I had a master metered park we had strict restrictions on what kind of appliances you could have etc. As much of the appliances that could be gas were required to be gas. Even with that- if everyone got an AC unit it would have blown our power supply.
The owner has good reasons to say no (probably). If the infrastructure can not handle the power it just can not.