So, EWROM comes with one 32 KiB RAM.
It's connected to the following
relevant signals from the MMC5:
PRG RAM 0 /CE,
PRG RAM A13,
PRG RAM A14,
PRG RAM /WE, and
PRG RAM Vcc, while the other 23 pins are just connected to pins on the cartridge connector.
ETROM and EKROM, instead, come with two or one 8 KiB RAMs. They're instead connected to
PRG RAM 0 /CE,
PRG RAM 1 /CE on ETROM,
PRG RAM +CE,
PRG RAM /WE, and
PRG RAM Vcc. Pin 1 on HVC-ETROM is tied to
PRG RAM Vcc, while on NES-ETROM it's tied to
PRG RAM A14.
To get a 64 KiB layout, you need
PRG RAM 0 /CE and
PRG RAM 1 /CE, one for each RAM, and
PRG RAM A13 and
PRG RAM A14 to address 32 KiB in each RAM.