Meanwhile, I just read in another post where someone said that "philo" is an
electrician. If that is correct, and if you do happen to know the answer to
my original question about how to wire a 110-volt interconnected alarm
system, that would be great. I think that I may already have that question
figured out, but if you know the answer, that would be helpful information.

to interconnect the alarms, you need a third wire run between the alarms.
The third wire is usually in the 14/3 i,e usually the "red" wire. It does not matter how the wire is routed, it does not have to be directly between the alarms, as long as it gets connected.

The hard part is that you probably have 14/2 running to the alarms and that would have to be replaced with 14/3. The third wires from each alarm could then be connected together wherever they meet. i.e in the breaker panel.

M