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Two optically obscured Wolf-Rayet (WR) stars have been recently discovered bymeans of their infrared (IR) circumstellar shells, which show signatures ofinteraction with each other. Following the systematics of the WR starcatalogues, these stars obtain the names WR\,120bb and WR\,120bc. In thispaper, we present and analyse new near-IR, $J$, $H$, and $K$-band, spectrausing the Potsdam Wolf-Rayet (PoWR) model atmosphere code. For that purpose,the atomic data base of the code has been extended in order to include allsignificant lines in the near-IR bands.  The spectra of both stars are classified as WN9h. As their spectra are verysimilar the parameters that we obtained by the spectral analyses hardly differ.Despite their late spectral subtype, we found relatively high stellartemperatures of 63 kK. The wind composition is dominated by helium, whilehydrogen is depleted to 25 per cent by mass.  Because of their location in the Scutum-Centaurus arm, WR\,120bb andWR\,120bc appear highly reddened, $A_{K_{\rm s}} \approx 2$ mag. We adopt acommon distance of 5.8\,kpc to both stars, which complies with the typicalabsolute $K$-band magnitude for the WN9h subtype of -6.5 mag, is consistentwith their observed extinction based on comparison with other massive stars inthe region, and allows for the possibility that their shells are interactingwith each other. This leads to luminosities of $\log(L/L_\odot) = 5.66$ and5.54 for WR\,120bb and WR\,120bc, with large uncertainties due to the adopteddistance.  The values of the luminosities of WR\,120bb and WR\,120bc imply that theimmediate precursors of both stars were red supergiants (RSG). This implies inturn that the circumstellar shells associated with WR\,120bb and WR\,120bc wereformed by interaction between the WR wind and the dense material shed duringthe preceding RSG phase.

WR 120bb and WR 120bc: a pair of WN9h stars with possibly interacting circumstellar shells