Big sis and Dad I saw them but they didn't see me

Got the shock of my life came home from baseball practice tired and in need of a shower. Did that and then crashed for a couple of hours woke up was going downstairs to see what everyone was doing. I got about four steps down the stairs and saw something I never would have expected my father was laid back on the couch my sister was kneeling between his legs jacking him off. I wiped the sleep from my eyes thinking this can't be what it looks like but I was wrong indeed it was Dad laid back his eyes closed in a relaxed state and my sister 16 only a year older than me slowly and methodically stroking his prick with one hand the other and then would switch every now and then. In looking at this it was easy to see this wasn't the first time this took place but I got tremendously turned on my little 15 year old cock stood at attention. I sat back on the stairwell and continued watching as they couldn't see me based on the angle of the staircase. This was the first time I had seen my father's cock and I was actually impressed. It looked to be larger than average by a little I guess regarding length but the girth it was one thick prick my sister continued massaging stroking first with one hand on the balls and the other pumping then she'd switch hands then she take both hands off his cock and massage his nuts there was no sound from him. Just laid back eyes closed.

I watch this for what seemed quite a while but in reality probably only 10 12 minutes. I was so hard I started rubbing my cock she started to pick up the pace and then I started to hear low grunting groaning sounds from Dad she now had one hand around the base of his thick cock and the other rapidly jerking the knob he let out a massive moan and then ejaculated shots of semen which my sister directed onto his stomach. You could see it run down her hands she kept the pace up for just a few seconds and she methodically expertly squeeze the base of his prick right to the head to get those last few drops.

I was so hot and turned on got to my room locked the door jacked myself off it took all of about 30 seconds it felt different when I shot my cum this time I can't explain it a lot of sperm and then I just relaxed and considered what I saw today thinking it must have been a dream but knowing it wasn't. Now I've got to find a way to maybe let my sister know I saw it in hopes she'll help me out