Does **rstanarm** allow using instrumental variable (conditional instrument in this case) for making an equivalent analysis to two-stage least squares? How to do it? Possible to do it with different types models, i.e. combining bernoulli, lognormal and survival?

**DAG**

Z is the conditional instrument when adjusting for P1-P3.

**EXPOSURE**

X - is a zero-inflated extremely positively skewed continuous variable. Does this 2SLS method allow me to use two models (binomial on all data and lognormal for positive values) in the first phase of analysis or I have to restrict the first phase to one model (binomial only)? In other words, can I go for plan A or B?

Y - is a survival object, including time and status

**A**

m1 = X ~ Z + P1 + P2 + P3, binomial model (all X values

m2 = X ~ Z + P1 + P2 + P3, lognormal model (positive values of X)

m3 = Y ~ fitted_probability_for_positive_X_values + fitted_positive_X_values + P1 + P2 + P3, survival model

**B**

m1 = X ~ Z + P1 + P2 + P3, binomial model (all X values

m2 = Y ~ fitted_probability_for_positive_X_values + P1 + P2 + P3, survival model

Rstanarm seemed not to have a lognormal family, can I combine brms and rstanarm models or they are too different things?

Everything that helps to proceed is really welcome.