As indicated already by G. Herold - forget the bias currents. These currents have only a minor effect on the circuits function.
Overall transfer function: It is not easy to read your drawing, but I guess the overall feedback resistors are R5 and R6, OK?
That means, your circuit contains a main amplifier A - consisting of two opamps (A1 and A2 with internal feedback) in series with an RC lowpass in between. Therefore, as a first step you should find the expression for the overall gain A. Then, as a next step, you apply Black`s feedback formula for the closed-loop gain Acl:
with k=feedback factor k=R6/(R5+R6) .
This gives you the gain referenced to the non-inv. input of the 1st opamp. As a final step, you can consider the passive circuitry at the non-inv. input.
Comment (edit): The first opamp in your circuit has no internal feedback. Therefore, if you assume ideal opamp properties (open-loop gain infinite) the gain A also will be infinite, and the closed-loop gain reduces to Acl=1/k. Otherwise (for real opamp properties), you must use the frequency dependent gain function for each of the two opamps.