The most basic simulation will be of the form:
(ds = \mu S dt + \sigma S dz)
where (\mu) and (\sigma) are your estimates of drift and volatility, respectively and (dz) is the stochastic processes.
In your case, though, since you have 2 series, you will have 2 processes:
(ds_1 = \mu_1 S_1 dt +...