Group tables and return in json

I have this function that returns the data for Ajax:

public function get_agenda(){
    $this->db->select('prospect_agendamento.age_data_agendado_para as start, prospect.pro_nome as title, prospect.pro_id as id ');
    $this->db->where('prospect_agendamento.age_data_agendado_para BETWEEN "'. date('Y-m-d', strtotime($_GET['start'])). '" and "'. date('Y-m-d', strtotime($_GET['end'])).'"');
    $this->db->join("prospect", "prospect.pro_id=prospect_agendamento.age_id_prospect");
    $retorno = $this->db->get('prospect_agendamento')->result();
    echo json_encode($retorno); 
}

So far, everything works perfectly. However, I need to add to this same return, another listing, which will compose json.

What would be of this table structure:

The other function I have to group is this:

public function get_agenda_1(){
    $this->db->select('tarefa.tar_data_inicial as start, tarefa.tar_data_final as end, tarefa.tar_titulo as title');
    $retorno = $this->db->get('tarefa')->result();
    echo json_encode($retorno);
}

How can I make a new list?