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I am not sure I understood your question correctly, but it seems to me that you are dealing with a case of a system with two simultaneous equations. For identification, you will need at least two instruments, for each endogenous variable of interest, and implement 2SLS estimation. If you want a more efficient estimation, you will need to make some additional assumptions on your error terms, in which case you can apply a 3 stage least squares estimator. The references are standard textbook ones (e.g., Wooldridge).
Yevgeniy
