  We investigate, within the fluctuation-exchange approximation, a
correlated-electron model for Y2Ba4Cu7O15 represented by two inequivalent
Hubbard layers coupled by an interlayer hopping $t_\perp$. An energy offset
$\delta$ is introduced in order to produce a different charge carrier
concentration in the two layers. We compare several single-particle and
magnetic excitations, namely, the single particle scattering rate, the spectral
function and the spin lattice as well as spin-spin relaxation times in the two
layers as a function of $\delta$. We show that the induced interlayer magnetic
coupling produces a tendency to ``equalization'' of the magnetic properties in
the two layers whereby antiferromagnetic fluctuations are suppressed in the
less doped layer and enhanced in the heavily doped one. The strong
antiferromagnetic bilayer coupling causes the charge carriers in the plane with
larger doping concentration to behave similar to those of the underdoped layer,
they are coupled to. This effect grows for decreasing temperature. For high
temperatures or if both layers are optimally or overdoped, i.e. when the
antiferromagnetic correlation length becomes of the order or smaller than one
lattice site the charge carrier and magnetic dynamics of the two layers is
disconnected and the equalization effect disappears. These results are in good
agreement with NMR experiments on Y2Ba4Cu7O15 by Stern et al. [Phys. Rev B 51,
15478 (1995)]. We also compare the results with calculations on bilayer systems
with equivalent layers as models for the constituent compounds YBa2Cu3O7 and
YBa2Cu4O8.
