While I've never done anything with a member of my family, I have been involved in some fun with some buddies that happened to be brothers.... Twice actually with different brothers and different girls.
Both instances happened in my hot tub. Both happened after a night of drinking. I was out with at a bar with Mike and Jeff (they're the brothers), we met some girls and took them back to my place for a dip. Before we knew it the two chicks were taking turns blowing the three of us in the hot Tub. Then it moved inside were me Mike and Jeff took turns railing them..... The girls LOVED it, as did I, especially the view. While none if us guys did anything, I do have fond memories of seeing Mike's cock in the chick's mouth while Jeff was fucking her doggy style. All three of them pretty much came at the same time. Jeff pulled out, ripped off his rubber and shot his load all over the girl's back. Mike blew his load in her mouth right after his bro. The girl obviously as she was wiggling and moaning like crazy!
The second time was with my neighbor Gregg and his brother (can't remember his name) Same scenario, met a girl in a bar, took her to my house for a soak in the tub. She made it pretty clear that she wanted to blow all three of us. It took her about 30 seconds before she was deep throating us. Again, fantastic sights seeing Gregg and his bro's hard dicks. Gregg probably has the biggest cock I've ever seen. Nothing happened between the guys except some unintentional contact between dicks while she was trying to take two at a time. She wouldn't let us nail her though.
There was a third time that I did not participate in, I just happened to see. One night I was getting home late. I did not have my key so I had to go through the back door where I had a spare hidden. Little did I realize that my roommate was messing around with some random on the back deck. That girl came around quite a bit after that, and one night (under the same circumstances) I found her blowing my roommate's little brother in the hot tub. I got my turn with her a couple weeks later.
I loved my 20's!