the Nest will only connect/trigger with other Nest detectors. if you existing hardwire smokes alarm goes off the nest can not silence them. if you just want a way to know remotely if there is a fire or CO issue then the Nest will work for that. if you want to make the house solely Nest then you need one in each bedroom, one outside in a common area of the bedrooms (hallway etc) one in living room/common area, garage, top of stair wells. contact your fire department to see what code would be if you would need additional units. but you are looking at >$500 easy.
another option is to get a Google home/alexa/homepod as they can be set to listen for your current smoke alarms and/or breaking glass and send you an alert to your phone.
No unsymmetrical camera bump.