Here i have a circuit where I need to find Q2 4μ seconds after switch closes:

Here is my work where i got so far and now i'm stuck what do next. First, did i take appropriate steps to get to Thevenin circuit and reattaching the load?

 

I assume your Vth and Rth are correct (haven't checked the calculations).

Then find the RC time constant of the equivalent circuit and find the voltage (Vctotal) across the total capacitance of the circuit at 4us.

Then use this to find the voltage across C2 and C3:

Vc23=Vctotal-Vctotal*(C2+C3)/(C1+C2+C3)

Then the charge Q2=Vc23*C2.