  Magnetic skyrmions are topologically protected spin textures with potential
applications in memory and logic devices. Skyrmions have been commonly observed
in systems with Dzyaloshinskii-Moriya interaction due to broken inversion
symmetry. Yet, recent studies suggest that skyrmions can also be stabilized in
systems with inversion symmetry such as Ni-based dihalides due to magnetic
frustration. In this article, we employ atomistic simulations to investigate
chiral magnetic phases in bilayers of NiI$_2$ and NiBr$_2$. We show that the
antiferromagnetic interlayer coupling introduces an additional magnetic
frustration and gives rise to a variety of novel spin textures with different
topological charges. Specifically for NiI$_2$, we observe that the skyrmions
with the in-plane component of spins wrapping around twice (biskyrmions) have
an enhanced stability compared to the monolayer case. We also study the
polarization induced by the non-colinear magnetic order in NiI$_2$ bilayers and
show that the polarization of the topologically nontrivial phases is negligible
compared to the spiral phases. Thus, we conclude that polarization measurements
can be an indirect route for detecting skyrmions in upcoming experiments.
