WhatsApp changes the way of Group calling in its latest interface of its iOS Version. However, it will soon roll out for Android users too. In the new interface or you can say update, You can start group calling by initially adding all the participants. Before, this update you have to first open the 1:1 group call and later you can add participants into it. However, it changes now.
Although the maximum number of participants that can be present in a group call is 4. A smaller number when we compare it to other apps belonging to same niche. For example, Messenger supports Group call upto 50 people whereas in case of Apple Face-time this number is 32.
To place a group call in this latest WhatsApp interface all you have to first go to the group whose members you wanna call. Once you open the group, at the top right corner you see a phone + icon. Tapping on it reveals a list of members. Now, you can select a maximum of 4 members. Once you select all the members, at the very top of member list you see video calling as well as phone icon both. Now, you can choose among these two option according to your need.
Note that the quality of WhatsApp video or voice call depends on the weakest network connection.