  High resolution heat capacity and thermal expansion experiments performed on
single crystalline kagome-staircase compounds (Co$_{1-x}$Ni$_x$)$_3$V$_2$O$_8$
are presented. The parent compounds Co$_3$V$_2$O$_8$ and Ni$_3$V$_2$O$_8$
undergo a complex sequence of first- and second-order magnetic phase
transitions. The low-temperature ($T<40$ K) magnetic entropy evolves
monotonously with the doping content $x$, from the full S=1 Ni$^{2+}$ magnetic
entropy in Ni$_3$V$_2$O$_8$ to half of the S=3/2 Co$^{2+}$ magnetic entropy in
Co$_3$V$_2$O$_8$. Thermal expansion coefficients $\alpha_i$ ($i = a$, $b$ and
$c$) show a strong anisotropy for all (Co$_{1-x}$Ni$_x$)$_3$V$_2$O$_8$
compounds. The low-temperature magnetic distortion indicates that Co-doping
(Ni-doping) has similar effects to applying a uniaxial pressures along $a$ or
$b$ ($c$). Linear Gr\"{u}neisen parameters $\Gamma_i$ are extracted for the
three main axes $i$ and exhibit a complex behavior with both temperature and
doping. For each axis, $\Gamma_i$ and $\alpha_i$ exhibit a sign change (at low
temperature) at the critical concentration $x_c\simeq0.25$, at which the
incommensurate magnetic propagation vector changes. Beyond our study, an
understanding of the multiple and complex parameters (magnetic frustration,
magnetic anisotropy, mixture of S=1 and S=3/2 ions, etc.) is now necessarily to
bring light to the rich magneto-elastic properties of
(Co$_{1-x}$Ni$_x$)$_3$V$_2$O$_8$.
