Create relationships for group with teacher / students

I'm trying to create the relationships between the models Group and User something like this but I'm unsure how to do it

Group
// I'm not sure if there are better in the GroupUsers Model or not

public function teacher()
{
    return $this->hasOne(User::class)->where(// check for user_type here of the group users and return the user type is 4)
}

public function students()
{
    return $this->hasMany(User::class)->where(// check for user_type here of the group users and return the user type is 5)
}

User

//this is the relationship I already have which gets all the group users
public function groupUser()
    {
        return $this->hasMany(GroupUsers::class);
    }

Any help is greatly appreciated !