I want to dim the lights in a bathroom chandelier. The chandelier has candle flame type bulbs and two switches for it. Do I need to install a dimmer on each switch?

Assuming you mean two wall switches. No, you only need to replace one of the switches with a 3-way dimmer switch. Does not matter which switch you replace.

No, you can't install 2 dimmers, they won't work. Install a 3 way dimmer on 1 switch and leave the other one alone.