I am new to the forum, so I don't really know if I should just jump right in, but here goes.
I too am in the same type of relationship, but our V are two women and one man. We have adult children. Six in total. I can't say it has been all sunshine and roses with our children, but they love us and are trying. I think the biggest concern for my partners' children was whether Mom and Dad are okay. Does my being there mean they love each other less? No. But things are different.
As for our families. Some know, some suspect and some have no clue. Mine have no clue. There are family members who have asked outright. They deserve the truth. We don't try to justify. We just state the truth as we know it to be for us.
As for the outside world. There is no doubt people suspect. We don't make a concious effort to hide it. If asked, we tell the truth. Which brings up alot of questions. Some that are asked because of genuine curiosity and interest, and some (mostly from men) because they want to know how we work out our sexlife. The questions asked because of genuine interest we answer. The others we don't.
We haven't found any hard and set rules for what is right and wrong. But we know to deny what we share takes away from all of us.
Are we ready to tell the whole world. Hell no. But we're figuring it out as we go along.