  Repeating fast radio bursts (FRBs) present excellent opportunities to
identify FRB progenitors and host environments, as well as decipher the
underlying emission mechanism. Detailed studies of repeating FRBs might also
hold clues to the origin of FRBs as a population. We aim to detect the first
two repeating FRBs: FRB 121102 (R1) and FRB 180814.J0422+73 (R2), and
characterise their repeat statistics. We also want to significantly improve the
sky localisation of R2. We use the Westerbork Synthesis Radio Telescope to
conduct extensive follow-up of these two repeating FRBs. The new phased-array
feed system, Apertif, allows covering the entire sky position uncertainty of R2
with fine spatial resolution in one pointing. We characterise the energy
distribution and the clustering of detected R1 bursts. We detected 30 bursts
from R1. Our measurements indicate a dispersion measure of 563.5(2) pc
cm$^{-3}$, suggesting a significant increase in DM over the past few years. We
place an upper limit of 8% on the linear polarisation fraction of the brightest
burst. We did not detect any bursts from R2. A single power-law might not fit
the R1 burst energy distribution across the full energy range or widely
separated detections. Our observations provide improved constraints on the
clustering of R1 bursts. Our stringent upper limits on the linear polarisation
fraction imply a significant depolarisation, either intrinsic to the emission
mechanism or caused by the intervening medium, at 1400 MHz that is not observed
at higher frequencies. The non-detection of any bursts from R2 implies either a
highly clustered nature of the bursts, a steep spectral index, or a combination
of both. Alternatively, R2 has turned off completely, either permanently or for
an extended period of time.
