Question about interconnected smoke and co detectors

This post was removed from r/fire alarms because I guess they voted and decided they didn’t want to answer smoke detector questions anymore 🤷‍♂️… but it was suggested to put it here.

We built our home in 2010 and we’ve got numerous smoke, co, and combo alarms throughout the home, all hardwired with battery backup, and we haven’t touched the configuration of the alarms until very recently. All of the smoke and smoke/co combo alarms in the home are first alert/brk except the co alarm in the boiler room and the co alarm in the basement area outside the boiler room which are kiddie. That’s how it was when the home was built and passed inspection and I’ve never changed the brands or types anywhere when it was time to replace.

Just recently I had to change the boiler room kiddie co alarm so I got a first alert smoke/co combo alarm and used the adapter to plug that in. I figured smoke and co would be safer plus I was having trouble finding kiddie at the time at local retailers. These alarms have never triggered before except low battery chirps so I tested it after install and only that alarm went off, nothing else in the home sounded (3 floors). Odd… so I went and tested the kiddie co alarm in the basement outside the boiler room and that only triggered the other smoke/co first alert alarms in the home. The other smoke detectors didn’t sound. I was excepting the whole home to start beeping but at least this one triggered one alarm per floor so we’d hear something.

I decided to take the basement co kiddie alarm and put it in the boiler room to test if maybe it was an issue with the alarm itself and still, only the boiler room sounded and nothing else in the home, not even the other smoke/co first alert combo alarms this time.

So now I have questions :(. Do different brand alarms not work with each other even when hardwired? Would a co alarm going off not also sound off all the other alarms if they’re interconnected or only sound off other co and smoke/co alarms? Not talking about if co would trigger a smoke detector but if the alarm on one floor going off would also make every other alarm go off. Lastly, would a boiler room alarm not be connected to the rest of the home for some reason? I’m in MA so is there some code I’m unaware of that would prefer it this way or not require that the boiler room co alarm is interconnected? I’m thinking about changing all the alarms to first alert now but the boiler room alarm isn’t connected either way as of now.

Sorry about the wall of text and thanks in advance for the help!