choosing a voltage regulator chip
Consider LTC3633A. I used it for several designs, it works very good, predictable and according to the datasheet. I suggest using MLCC X7R or X5R for input and output filters (no aluminum or tantalum capacitors!) and running it about 2.5-3.2 MHz.

Two or three "layers" of LC or LRC filters are enough to meet RF requirements for interference. Make sure that the filters have no high Q resonances at any frequency. The PCB design is of major importance: pay a great attention to locate switching currents of each power stage inside a very small area near the chip and its capacitors. Use large current ferrite beads to isolate 12 power supplies to each switching regulator.

However: 1.2 V precision will be greatly compromised by PCB traces / connector resistance. It is better to use local (point-of-load) power supplies for such a low voltage.