  There are valuable arguments to perform neutrinoless double beta
($0\nu2\beta$) decay experiments with several nuclei: the uncertainty of
nuclear-matrix-ele\-ment calculations; the possibility to test these
calculations by using the ratio of the measured lifetimes; the unpredictability
of possible breakthroughs in the detection technique; the difficulty to foresee
background in $0\nu2\beta$ decay searches; the limited amount of isotopically
enriched materials. We propose therefore approaches to estimate the Majorana
neutrino mass by combining experimental data collected with different
$0\nu2\beta$ decay candidates. In particular, we apply our methods to a
next-generation experiment based on scintillating and Cherenkov-radiation
bolometers. Current results indicate that this technology can effectively study
up to four different isotopes simultaneously ($^{82}$Se, $^{100}$Mo, $^{116}$Cd
and $^{130}$Te), embedded in detectors which share the same concepts and
environment. We show that the combined information on the Majorana neutrino
mass extracted from a multi-candidate bolometric experiment is competitive with
that achievable with a single isotope, once that the cryogenic experimental
volume is fixed. The remarkable conceptual and technical advantages of a
multi-isotope investigation are discussed. This approach can be naturally
applied to the proposed CUPID project, follow-up of the CUORE experiment that
is currently taking data in the Gran Sasso underground laboratory.
