The scopes of the two groups should intersect and agree in their intersection, but can each involve areas independent of the other.

Possible scopes might be:

for the elderly

(a) common interface(s) for all assistive technology within residential setting
(b) the same but within sheltered housing setting (where one may have built-in infrastructure and purpose built design)
(c) the same but in subject's own home (additions to generic housing)
(d) focus on emergency alarms and automatic sensors, but in any of the above environments

For the carer

(i) general call centre dealing with range of settings: night-care in residential accommodation, sheltered housing or home
(ii) interfaces for wardens of large residential home including carry-about PDAs, central desk, home night alarms

looking at these (a) and (ii) would obviously match (identical setting), but (c) and (ii) would not be an acceptable pair of scopes (no intersection). However, (i) would be work with any of (a-c) (intersecting scope).

In each of these cases facilities within common scope must agree. For example, if we were in (a-i) and the elderly side assumed the permanent availability of a video link to the warden, then this would need to be catered for at the call centre. You can use scenarios etc. to help you reach this consensus.