In HTML require to have:
<script type="text/javascript" src="/_layouts/15/sp.runtime.js"></script>
<script type="text/javascript" src="/_layouts/15/sp.js"></script>
<script type="text/javascript" src="/_layouts/15/clienttemplates.js"></script>
<script type="text/javascript" src="/_layouts/15/clientforms.js"></script>
<script type="text/javascript" src="/_layouts/15/clientpeoplepicker.js"></script>
<script type="text/javascript" src="/_layouts/15/autofill.js"></script>
Add user to PeoplePikcer:
key is 'domain\\loginName' or user mail
SPClientPeoplePicker.SPClientPeoplePickerDict['peoplePickerId'+"_TopSpan"].AddUserKeys(key);
To remove all users:
SPClientPeoplePicker.SPClientPeoplePickerDict['peoplePickerId'+"_TopSpan"].DeleteProcessedUser();
To prevent add multiple time the same user:
SPClientPeoplePicker.SPClientPeoplePickerDict[peoplePickerElementId + '_TopSpan'].OnUserResolvedClientScript = function (peoplePickerId, selectedUsersInfo){
var users = selectedUsersInfo;
for(var i = 0; i < users.length - 1; i++) if(users[users.length - 1].Key == users[i].Key) this.DeleteProcessedUser();
};