Fireplaces, Heating Stoves, Flues and Chimneys - Interior Brick on Woodstove. Mortar outside

We have falling brick IN our woodstove, which is 30 years old. Do the replacement bricks need to be mortared in? The stove also doesn't draw well anymore. We have previously cleaned it ourselves (son) with a chimney sweep broom. Should we have a professional clean it and replace the brick inside? We have cracks in the mortar on the outside also (I wrote another post re this and MANY other things). Can homeowners remortar brick safely themselves outside? This is our primary heat in winter for the kitchen and family room; and the heat goes down the hall to help with the back. However, it has been unpleasant in recent year or two to burn ... In fact, we didn't use it last winter at all. We relied on occasional use of portable heaters as our main gas heater/air conditioner needs replacing. Thanks much for any input

Call a chimney pro ASAP for cleaning and inspection. As you describe the condition of the chimney, do NOT use until repairs are made. Chimney will likely have to be lined, crown replaced/repaired, and capped. Repointing of exterior brick can be DIY.