Who should be asked to be a bridesmaid

You are not obliged to have anyone in your wedding party - it's entirely up to you! If your husband-to-be thinks that his granddaughter might be upset not to be included, you could always find a small role for her - e.g. perhaps handing out orders of service. But not every small girl dreams of being a bridesmaid anyway - I had to be one for my cousin when I was about that age and hated every minute!!! So she might be happy just to be a guest.