How can i insulate exterior brick walls
Either build in, or build out.

Out will cause less disruption, normally. Exterior Insulation and Finish System (EIFS) is a generic term for the typical approach, which consists of applying insulation (typically foam board) and a protective finish (typically stucco.) This is quite common in commercial construction.

Building in will reduce the size of your rooms and require all rooms with an exterior wall to become construction sites as the work progresses. Additional work will be needed to extend any electrical (switches, receptacles), plumbing fixtures or HVAC vents from the old walls to the new walls. It will probably cost more, as well.

If the house is "historic" you may have additional considerations/restrictions.