Open Settings → Avatar or use your account/profile photo options to update your picture.
Yes. JoinPeoples supports Google Login.
Open Settings → Post Privacy to manage your post visibility.
You can block the user and use the available report controls for problematic users, posts or comments.
Check Notification Settings and make sure the notification types you want are enabled.
Open Settings → Password & Security and use the password change option.
Contact JoinPeoples support and describe what happened, what you expected and what you tried.