No. It is not possible to actively use the same OtoZen account on two different devices simultaneously.

If you are logged in to your OtoZen account on one phone and then log in to the same account on another phone, you will be logged out from the first phone.

OtoZen accounts are linked to a phone number, so each family member should use OtoZen with their own phone number and their own account.

Different family members can still use OtoZen on different phones, as long as each person is using a separate OtoZen account linked to their own phone number.