I would be putting both in LC and SCB modes to reduce load on the panel.
Without checking with a multimeter you have no way of knowing the system load and if the standby battery is adequate.
You need to use 360 PIR's that are designed to connect to an intruder alarm system.
Many manufacturers make 360's, from memory the most discrete being Scantronic 450, if they still make them.
There are companies listed here you can try.
http://www.thesecurityinstaller.co.uk/community/forum/268-uk-security-installers-by-regional-police-force/
Add these URL's to your Content manager.
http://winhelp2002.mvps.org/hosts.txt
The issue with host blocking instead of adblockers are it can silently grind your browser to a halt if the site needs to load a blocked URL.
If existing is fault free and it's a basic system. Simple as plugging in coax to new DVR and wiring up a 12 volt supply.
Other than physically coming out there to do it, there's not a lot to assist with.
http://arstechnica.com/information-technology/2016/05/microsoft-bangs-the-final-nail-in-nokia-devices-coffin-fires-the-last-1850-workers/
FYI for those of you that use them.