Sorry to hear about your brother and his little girl.  It's always sad to have someone pass before their time.

Now, load your brother's track in MMM and go to the Templates tab. In the effects presets you should find one called "Karaoke".  Click and drag Karaoke onto your track in the arranger and give it a few seconds to process.  That "should" remove most, if not all, of your brother's original vocals.  However, I've found that the Karaoke feature does not work as well with deeper male voices, but it's worth a try anyway.  Also, it will alter the frequency balance of the track, so you'll have to decide if you like the results.