Let X,Y,Z be random variables jointly distributed on the same probability space then we know the conditional probability $P(X=a,Y=b|Z)$ is a random variable which is $Z$ measurable. Can we say

$$P(X=a,Y=b|Z)=P(X=a|Y=b,Z)P(Y=b|Z)?$$

Moreover is it true to say

$$E[P(x=a,Y=b |Z)]=P(x=a,Y=b)?$$