Transceiver Supply isolation with Transformer
The data sheet tells you how to do it: -



It uses an SN6505 transformer driver.


  can I wire the 5V at pin 4 and the 3.3V at pin 2 of the transformer
  with pin 3 and pin 1 connected to their respective digital ground and
  connect the Vcc2 of the first transceiver at pin 8 and the Vcc2 of the
  second transceiver at pin 6 (with pin 7 and 5 of the transformer
  connected to their respective GND)?


No, it's a transformer and it requires an AC voltage drive and a rectifier on the output followed by a regulator to produce Vcc2.


  and I can't use other dc/dc isolated converter for the Vcc2


You have to find a way that allows this to happen. You either: -


use what TI recommends
find a different CAN bus transceiver that has isolated power transfer built in
use a DC-to-DC converter such as from Traco etc..