I want to run a new cable from my consumer unit to pick up 2 CO alarms and 4 smoke alarms:

Is a 1.5mm cable from a spare 16A MCB okay?
Does the cable need to run from alarm to alarm (i.e. radial) or can I run a single cable to the furthest one and spur off at 4 points for the other? (the later would use much less cable)
If I did the latter, would it cause problems?