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We analyse the $\overline B_s^0\to K^+l^-\bar \nu$ and $\overline B_s^0\toK^{*+}(\to K\pi)  \ell^-\bar \nu$ decays that are valuable for extracting the CKM matrixelement $|V_{ub}|$. We calculate the differential and integrated partial widthsin units of $|V_{ub}|^2$ based on various calculations of hadronic form factorsand in particular the latest Lattice QCD calculation of the $B_s\to K^*$ formfactors. For the decay $\overline B_s^0 \to K\pi \ell\bar \nu$, we formulatethe general angular distributions with the inclusion of the variouspartial-wave $K\pi$ contributions. Using the results for the $K\pi$ scalar formfactor calculated from unitarized chiral perturbation theory, we explore theS-wave effects on angular distribution variables and demonstrate that they maynot be negligible, considering the high precision expected in futuremeasurements. We also briefly discuss the impact of the S-wave $\pi\pi$contributions in the $B^-\to \pi^+\pi^-\ell \bar \nu$ decay and provideestimates for the mode $B^-\to K^+K^-\ell \bar \nu$. The studies of thesechannels in future can not only be used to determine $|V_{ub}|$, but may alsoprovide valuable information on the $K\pi$ and $\pi\pi$ phase shifts.

${\bf B_s\to K^{(*)} \ell\bar \nu}$, Angular Analysis, S-wave Contributions and ${\bf |V_{ub}|}$