  The nearby spiral galaxy NGC 3147 hosted three Type Ia supernovae (SNe Ia) in
the past decades, which have been subjects of intense follow-up observations.
Simultaneous analysis of their data provides a unique opportunity for testing
the different light curve fitting methods and distance estimations. The
detailed optical follow-up of SN 2021hpr allows us to revise the previous
distance estimations to NGC 3147, and compare the widely used light curve
fitting algorithms to each other. After the combination of the available and
newly published data of SN 2021hpr, its physical properties can be also
estimated with higher accuracy. We present and analyse new BVgriz and Swift
photometry of SN 2021hpr to constrain its general physical properties. Together
with its siblings, SNe 1997bq and 2008fv, we cross-compare the individual
distance estimates of these three SNe given by the SALT code, and also check
their consistency with the results from the MLCS2k2 method. The early spectral
series of SN 2021hpr are also fit with the radiative spectral code TARDIS in
order to verify the explosion properties and constrain the chemical
distribution of the outer ejecta. After combining the distance estimates for
the three SNe, the mean distance to their host galaxy, NGC 3127, is 42.5 $\pm$
1.0 Mpc, which matches with the distance inferred by the most up-to-date LC
fitters, SALT3 and BayeSN. We confirm that SN~2021hpr is a Branch-normal Type
Ia SN that ejected $\sim 1.12 \pm 0.28$ M$_\odot$ from its progenitor white
dwarf, and synthesized $\sim 0.44 \pm 0.14$ M$_\odot$ of radioactive $^{56}$Ni.
