Schematic for a lipo battery bleeder overcharge protector
Your proposed Overvolt protection      circuit is really an amplified zener and it could be set to say 4.2 volt and work .Now to do this properly you must shut down the charger or drastically reduce the charging current when one of your bleed off LEDs starts glowing .You have chosen to use 3 cells in your battery where most others in my neck of the woods use 4 .It would be tempting to buck down or even do a simple low drop linear reg given that you chose 3 cells .If you want to use a fet instead of a BJT you will have to get a very very low threshold device to operate correctly in your circuit.A garden variety PNP BJT or darlington will work fine .Your resistor values are a plausible start but fuse like the comment from mkeith said.Remember that not all TL431s are equal.The TL431 is in the www.badbeetles.com website .