Paying back a debt

My Aunt Robyn 37 owed my mother quite a bit of money, Robyn had lost her job and so needed a place to live till she got another job. My mother let her stay with us; my father had left us very well off when he suddenly died in a light plane accident. Thru inherited wealth and his career as well as a very large insurance payout, we were left quite well off. I'm not great with girls get too nervous and seen to be awkward. My mother believed I just needed more confidents. So, with her younger sister staying with us till she got another job. My mother decided to have Robyn teach me to be comfortable around girls. I was already comfortable my mother, so she thought her sister who I was slight nervous around would be a better tutor for. Both my mother and aunt are very attractive women for their ages. I don't know how they came to an agreement on my training, I just know they did. At 21 and still a virgin, nervous around girls wasn't what my mother wanted for my future as she wanted grandchildren. Robyn was divorced had a miscarriage during her marriage and was told she would never be a mother. So, with Robyn agreement I was being tutored by her, and it include sexual intercourse. Once I got over the shock and my own nervousness, I embraced the training whole heartedly. One unforeseen problem rose after several months of training, Robyn who hadn't bothered taking any precautions got pregnant. Shocking the three of us at first, I wasn't bothered at all getting my aunt pregnant. My mother's shock was replaced by her desire for grandchildren fairly quickly. Robyn also got over the shock and decided as all test showed the baby to be very healthy to have our child. The doctor hadn't said she couldn't ever have a child, just it was very unlikely. I remarked that it was because we weren't trying to have a baby, that it took some stress off her reproductive system and that allowed her to get pregnant. Needless to say, my mother is delighted and still somewhat shocked. Robyn has fulfilled their agreement as far as my mother is concerned, Robyn still sleeps with me however as she likes sex and I'm always willing. To annoy my mother however she asked her to join us in a threesome. At first my mother was shocked, but as she is passed having children she finally agreed, however she went on the pill beforehand just in case.