Distribution of circuits for two bathrooms
You are correct that the first two options are allowed by Code (citing from the 2014 NEC here) -- the relevant passage is 210.11(C)(3) along with its Exception:


  (3) Bathroom Branch Circuits. In addition to the number of branch circuits 
  required by other parts of this section, at least one 120-volt, 20-ampere 
  branch circuit shall be provided to supply a bathroom receptacle outlet(s). 
  Such circuits shall have no other outlets.
  
  Exception: Where the 20-ampere circuit supplies a single bathroom, outlets for 
  other equipment within the same bathroom shall be permitted to be supplied in 
  accordance with 210.23(A)(1) and (A)(2).


However, this passage only applies to receptacles unless you take advantage of the terms of the exception; putting the bathroom light on a shared lighting circuit is Code-legal as long as the receptacles are on a dedicated circuit.

For the heaters, you can either put them on a per-bathroom circuit as long as they satisfy 210.23(A)(2) by not using up more than 50% of the circuit's ampacity:


  (2) Utilization Equipment Fastened in Place. The total rating of 
  utilization equipment fastened in place, other than luminaires, shall not 
  exceed 50 percent of the branch-circuit ampere rating where lighting units, 
  cord-and-plug-connected utilization equipment not fastened in place, or
  both, are also supplied.


or you can have them on a shared lighting circuit, if you decide to have a separate circuit for bathroom receptacles.  Unfortunately, putting them on the same circuit as the bathroom receptacles when that circuit is shared between bathrooms is prohibited by the Exception to 210.23(A):


  Exception: The small-appliance branch circuits, laundry branch circuits, and 
  bathroom branch circuits required in a dwelling unit(s) by 210.11(C)(1), (C)
  (2), and (C)(3) shall supply only the receptacle outlets specified in that 
  section.