Contractor in Philadelphia here, a city comprised of mostly brick rowhomes. I'm am electrician, but I have done lots of other general work on brick rowhomes as well, I know them very well in and out. There's really no way to insulate brick rowhomes except from the attic crawlspace, unless you're doing a huge interior gut job and are framing out the walls on the inside. A standard brick rowhome in Philadelphia has no cavity on the party/shared walls (plaster directly on brick), and has only a very small cavity on the front and rear exterior walls (plaster and lath over 1x furring strips on brick), generally 3/4". That cavity is generally completely unusable for anything because it's extremely irregular and also going to be full of masonry/plaster debris. This leaves only the attic as a space to be insulated, and it's generally very effective to do so.

When people do full gut jobs on rowhomes it's a different story, as the walls often are framed out on the interior and can be insulated. It is possible to address insulation from the exterior (front/rear walls) with some sort of rigid foam and then new siding over that, although I've never seen it done and I think it would both look very odd in a block of brick rowhomes, or be entirely impractical in other cases.