Joint sampling PDF of sample mean and sample variance

Question

so if random samples $X_1,X_2,X_3$∼b(1,p), the Bernoulli parent with unknown parameter given by the success rate p∈[0,1] how would you obtain the joint sampling PDF $p_{\bar X , s^2}(\bar x, s^2;p)= P(\bar X = \bar x , S^2 = s^2)$ of the sample mean $\bar X= \frac13 \sum_{i=1}^3 X_i$ and sample variance $\mathit S^2=\frac12 $ $\sum_{i=1}^3 = {(X_i - \bar X)}$ ?