The partition function is defined as a sum over all microstates $j$ as:
$Z=\sum_{j}exp(-\beta E_j)$
or
$Z=\int_{-\infty}^{\infty} exp(-\beta E)dE$
if the states are continuous.
We can use $Z$ to get the probability $p_i$ that a system has microstate $i$ via:
$p_i=\frac{exp(-\beta E_i)}{Z} $
Now, does this work for finding the probability that a system is in multiple states?
For example, does
$p_{1,2}=\frac{exp(-\beta E_1)+exp(-\beta E_2)}{Z} $
define the probability of the system being in states $1$ and $2$?
If we have continuous states between $E_1$ and $E_2$, does
$p_{1,2}=\frac{\int_1^2 exp(-\beta E)dE}{Z} $
define the probability that the system has a microstate between states $1$ and $2$?