Semileptonic $B\to\pi\ell\nu$, $B\to D\ell\nu$, $B_s\to K\ell\nu$, and $B_s\to D_s\ell\nu$ decays.

We present updates for our nonperturbative lattice QCD calculations to determine semileptonic form factors for exclusive $B\to \pi\ell\nu$, $B\to D \ell\nu$, $B_s\to K\ell \nu$, and $B_s\to D_s\ell\nu$ decays. Our calculation is based on RBC-UKQCD's set of $2+1$-dynamical-flavor gauge field ensembles. In the valence sector we use domain wall fermions for up/down, strange and charm quarks, whereas bottom quarks are simulated with the relativistic heavy quark action. The continuum limit is based on three lattice spacings. Using kinematical $z$ expansions we aim to obtain form factors over the full $q^2$ range. These form factors are the basis for predicting ratios addressing lepton flavor universality or, when combined with experimental results, to obtain CKM matrix elements $|V_{ub}|$ and $|V_{cb}|$.