One could be a decoy box or both could be.ADT sometimes put decoy up outside with live sounder inside.
You would need to check if bell boxes a live units and not decoys.
How easy is it to get cables to these boxes.
Mite be easier to go with wireless system.
I would expect any wired or hybrid alarm control panel would work with that bell box.
Might be worth changing for up to date bell box, has you do not know how old the existing unit is.
You'll need to work out the combined current consumption, as many smaller panels may not be able to drive both sirens if they don't support SAB mode. Panels with a robust PSU like the Galaxy Dimension would be capable but perhaps a bit overkill for the premises.
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