Let $\K$ be a field of characteristic zero and $\Kbar$ be an algebraic closure of $\K$. Consider a sequence of polynomials $G=(g_1,\dots,g_s)$ in $\K[X_1,\dots,X_n]$, a polynomial matrix $\F=[f_{i,j}] \in \K[X_1,\dots,X_n]^{p \times q}$, with $p \leq q$, and the algebraic set $V_p(F, G)$ of points in $\KKbar$ at which all polynomials in $\G$ and all $p$-minors of $\F$ vanish. Such polynomial systems appear naturally in e.g. polynomial optimization, computational geometry. We provide bounds on the number of isolated points in $V_p(F, G)$ depending on the maxima of the degrees in rows (resp. columns) of $\F$. Next, we design homotopy algorithms for computing those points. These algorithms take advantage of the determinantal structure of the system defining $V_p(F, G)$. In particular, the algorithms run in time that is polynomial in the bound on the number of isolated points.