Living Far from the Grid

I'm David 21 single, I live in a very remote location. I live in a solar powered cabin with my mother Grace 42 and her partner Linda 39. The cabin is small 9 by 12 meters and has an outside toilet 30 meters from the backdoor. I have a pullout bed at the front of the cabin and they have an loft bed above the kitchen. I work with my mother mainly because she's all the family I've got. My father cleared out before I was born and there is no one left on my mothers side as she was a only child and her parents have passed away. Grace works for an university and likes to live in this region for the clear skies and because it has rare species to study. I live here because I like to paint landscapes and help Grace by doing the heavy work for them. Grace is 5'4" and Linda is 5'1" both slender, Linda is also here for rare species. But she is a botanist also likes to paint. I can hear then when they are making love in there loft bed. I have seen both naked and I do get a stiff thinking of them, just over 4 months ago I heard them lovemaking and so I started to masturbate. Then there was a loud noise from outside the cabin and everyone jump out of to investigate. I still had my cock sticking out of my boxer shorts and they had there nothing on under their open robes. It turned to be the old tree near the cabin had fell over hitting 2 empty fuel drums stored near it. It was too far from the cabin have hit it. On returning inside, Linda noticed my still rigid cock and asked what got you excited David. Not one to back away, I said Hearing you 2 go at it for one thing. Grace said Sorry to disturb you. Linda added Would you like to join us David with a cheeky grin on her face. Grace was shocked and when I answered I would like that very much I thought she might faint. Linda then said Do you think your able to service me well then. I answered Very well, Linda wasn't about to back down, so she added Will you fuck your mother too. I replied Yes, if she wants me too, Linda replied Oh she wants a good fucking she does really. Grace then said Well we going to Fuck or stand around here all night talking about it. I replied Lead the way, so Linda turned and climb the ladder to the loft followed by Grace then me. Once the loft, Linda told to strip and lay on back on the bed and she would do all the work top as didn't want any man on top of her. So I did and she went down on me and after climb on to me and I had sex with her. Grace was sucking her breasts and kissing her. I told them both that I was close to cumming, but they weren't hearing me and I came inside Linda. She didn't mind and I thought that she must have been on the pill on something. Then Linda told Grace was her turn a she went down on me and soon had me hard again. When I got close again I told her and she was going to get off. But Linda said Don't get off, take it inside you. Like I did. So she did. We all have had regular sex together since without me cumming inside them. A couple of weeks ago while in the city they got a couple of testing kits and that night they showed both were positive. So we sat around talking about it and it was decided for both to have their babies and Linda and Grace are to marry next trip to the city in a weeks time. I still sleep with them both and couldn't be happier.