As long as you know what you are doing, having two shocks simultaneously is no problem (and does in particular not contradict the logic of an IRF as it can be interpreted as a single new shock that hits two different variables at the same time) and can be done in Dynare. Moreover, it is a recurring theme. For a potential solution, see [3 exogenous shocks at a time). In case you want to use two different but correlated shocks, Dynare performs a Cholesky decomposition, see [Correlated shocks and impulse response functions)