Yes, you can use Google Duo or Google Meet to video call an iPhone user. These apps work across different platforms, so they can connect Android devices, including Samsung phones, with iPhones or other devices that support these apps.
Regarding FaceTime, iPhones typically only support FaceTime calls between Apple devices. However, Google Duo and Meet allow you to call iPhone users, even though FaceTime itself is limited to Apple devices.
So, no, iPhone users don't need multiple FaceTime apps on their phones. They can simply use FaceTime for calls within the Apple ecosystem or use a cross-platform app like Google Duo or Meet for calling across devices.