I have some advice for you...
We recently experienced exactly what you are talking about.
My wife and I have a mutual friend that comes to visit almost every weekend. It was obvious to me they had a natural attraction for each other from the start. It seems like every time we got together, the conversation revolved around sex.
Then about 2 months ago, they began to playfully touch each other while we were visiting, drinking and teasing each other. This led to kissing and feeling while I was out of eyeshot.
Never being fooled for a moment, I asked my wife if she wanted to fuck him. She said that she did but she was worried about some of the consequences that might arise within the family. You see, our mutual friend is 18 years younger than she is and one of our daughters expressed fleeting interest in this man at one point.
At any rate, I told her that is was OK for them to have sex as long as I was present. I told our friend the same thing. After that, things progressed slowly but in a definite direction. They began to show affection openly while I was present and they would do a lot of heavy petting.
3 weekends ago, he began going to bed with us when we did. The first time, he was quite nervous and everyone just ended up passing out on each other. The next morning, I had to go to work early while they both remained in bed. I must admit that I wasn't entirely comfortable with the whole situation but I figured that there was nothing I could do if it was going to happen so I didn't let it bother me. When I got home that afternoon, I was assured that nothing happened. I still don't know but I did say it was alright.
The weekend before last it want a lot futher but we were outdoors and it was pitch black outside so I didn't see anything but there was a lot of heavy breathing going on.
Then finally last Saturday night, it happened. When he went to bed with us we played all night and she gave him one hellacious cock sucking while I ate her but nothing really good happened until the early hours of the next morning.
I woke up on one side of my wife, and he was on the other. I could feel her hips gyrating so I knew he was fingering her. She began to breathe heavy so I began to stroke her back to reassure her that everything was alright. Then he quietly slipped his cock inside her from the backside and slowly began to stroke while I kneaded her tits and kissed her. She was laying on her side and it was very easy for her to go down on me; and that is exactly what she did.
I could only take that for about 5 minutes before I blew my load into her mouth. She swallowed every drop.
Now that I was done, I watched as they tried to finish each other off. It didn't go very well because the boy is fairly inexperienced. At one point she said, "Slow It Down Rabbit Boy!" They tried a couple of different positions but neither one of them was quite able to manage. I decided to lay there and smoke a cigarette and watch while they tried to work things out.
By the time I was done, they were still having trouble so I maturbated my wife while he jerked off beside her.
Even though things didn't go very well, it was a very erotic experience for all of us. Now they are more determined than ever to make it right. And as for my part, I am more than willing to help. He will be here again this weekend and we are going make it better for all now that we know what we are working with.
So my advice to you would be to take it slow and permissive. When the time is right, everyone will be willing and eager. It might take a few times but if you are like us, you will learn what works and what doesen't. Then you will all be happy.
I posted some of the pictures I took of our funny little threesome on this forum in Wife Pix under the title "I need some help!" if you are interested.
Take your time and good luck!
doc94