I have a few questions regarding accent LEDs and the resulting resistors I would need for them.

1)I have a few LEDs lying around the house I'd like to use, and while their currents are the same at 20 mA, their forward voltages differ from 1.8 to 3.7. can I use these in a parallel circuit with one resistor or would they have to have separate resistors? I used someones resistor calculator, but I couldn't enter two different voltages.

2) Would my layout from #1 be affected if I added a illuminated switch? How so?

3) Assuming everything has made sense so far, could someone help me find the proper resistor needed. I currently have a four AA battery back I could use, but I can order a different battery back if necessary.

Thanks for the help.