Started with my grandmother

I was 19 when this all started, I live with my divorced mother 38 and I was attending the local college. Financially secure thru trust fund and with additional money coming from an online business. Likewise, my mother is financially secure from inheritance and some alimony from my father, who isn't interested in me much if at all. Sees me as the reason he'd to marry my mother in the first place. Anyway, I was required by my mother to maintain her mother's yard. No hassles it was an easy task, mostly mowing and some old branches removal. My grandmother 56 is a very active woman, looks good for her age I think anyway. My mother went away on a trip with some friends to Las Vegas (4days) early Friday thru to late Monday. So, I was to stay with my grandmother (gran) she would cook my meals. I could go out if I wanted too, but I'm not big on going out that much. After college I arrived at my gran's home, helped her with dinner and the cleanup afterwards. Started an assignment I'd to do, then slept until woken for breakfast. After breakfast I mowed her lawn and removed dead branches off her fruit trees. That took about an hour from getting out the mower and putting it back. Gran was exercising in her leotards, when I entered her house. As I said I think she looks good and, in her leotards, she looked even better, and I got aroused. In just shorts and a T-shirt it showed, and gran seen it almost straight away. Made some jokes about me getting aroused over an old bird like her. But she than asked me to show her my erection, she started to stroke it and told me she'll get me off and led me to her bed. First, she just continued to stroke it and then she started to suck it getting me to blow my load and she took it all in her mouth and then swallowed it all. Kept playing with cock until it regained its hardness then mounting me and rode me until I came again. She was my first fuck and first blowjob, lucky for me my assignment was due in 14 days not on the morning. As I didn't touch it again that weekend, fucking my gran filled my time. Slept with her until I went to college on the Monday and then back home to my mother. Every weekend I would visit my gran, and most times got sex. After a couple of months my gran went to visit her sister, I was left with nothing to fill my weekends I thought I'd been visiting my gran every weekend till then. But I wasn't going to miss out as it were, my mother had noticed my extra zeal in visiting her mother. Had talked to her mother who straight out told her I was I fucking her, for our mutual benefit. My mother at first was somewhat shocked, but she knew it wasn't causing either of us any harm, so it let continue without any fuss. But her mind also got excited by idea of forbidden sex as they say, with her mother away. She knew I wouldn't be going anywhere, so after dinner on the Friday my gran had left. I was in my room reading a book for another college assignment. When my mother came in wearing her bathrobe, letting it drop to the floor revealing her to be totally naked. She said you're fucking my mother, how about fucking yours as well. I was shocked a little at first but recovered quickly, my mother became the second I've fucked. Like with my gran we fucked all weekend and during the week following. Only had one accident when a condom broke inside my mother, not to concern by that. On my grans return we'd a threesome and gran put her house up for sale and moved in with us. Several weeks later, mother felt off she said. I thought she might come down with the flu or something. Instead, she was pregnant and would've my sister/daughter. No real concerns after the baby was pronounced healthy by the doctor. Now 3 years later, my mother is the last trimester of her second pregnancy to me and is having a boy. No accident this time, it was planned by the three of us, my daughter 2+ is very excited about having a little brother. Still fucking my gran.