If you cannot get WhatsApp working, try these which still support legacy iOS:
A: Yes, if you install the last compatible version via Purchased history. But expect it to become non-functional within 6–12 months. whatsapp old version for ios 9.3.6 download
Back in the day, WhatsApp was compatible with older iOS versions, but as the years went by, the app received updates that made it incompatible with older iOS versions. If you cannot get WhatsApp working, try these