As we used to say in the world of technical authorship, 'If all else fails, read the instructions'.
DfT contract spec for Lot 1:
"minimum rescue capacity per Aircraft of 8 Casualties/Survivors (2 of which are capable of being stretchered)"
Bristow SAR website, fleet section, Sikorsky S-92, stated capacity:
"21 persons as required – 3 stretchers, 10 seated persons, additional standing persons"
Bristow SAR website, fleet section, Sikorsky S-92 illustrations:
http://bristowsar.com/wp-content/upl...-survivors.jpg
http://bristowsar.com/wp-content/upl...figuration.jpg
http://bristowsar.com/wp-content/upl...ernal-view.jpg