Two guys in a tub. Next thing you know one wakes up and one is dead.
laser pointer
Flatlined, when I let you borrow my binoculars, it wasn’t for this.
Cite for pix?
Never mind him- is she a good sort?
Carl.
Are they masturbating like motherfucks and/or loudly proclaiming this fact?
'Cause that would be the tipoff for me.
flatlined–now, how tall is the box you are standing on to see this, again?
(In your opinion.) Does it look like you’re the only one, that could possibly see this? If they’re assuming that no one else can see their <ahem> ‘activities’, then it’s reasonable to assume that they think they’re hidden from casual view. Maybe they just didn’t fully observe all of the different “lines of sight” that were possible. (Then again, maybe they did!;))
If you feel the need to let them know, you could invite them over and show them your yard, which includes the view. Hopefully they catch on.
That’s the vibe I got from the OP. It appears to her that they are trying to be private but just failing due to someone being overly observant.
I also would say that, if I, as a guy, did this, I would be considered a horrible pervert. Even if they want to expose themselves, the fact that I’m watching in secret would be enough for most people. And I heavily dislike different standards for men and women.
So while I don’t care whether you tell or not, if you don’t. I would say you should stop watching. If you want to keep watching, then come up with some way to let them know, even if it’s less direct than flat out telling them.
Here’s one idea: In casual conversation at some point, talk about that their deck looks really neat, thus indicating you can see it. (If they don’t get it, mention seeing happening to notice you can see it from your front porch.) It sounds like you have enough of an acquaintanceship to pull that off.
They didn’t have any idea that I could see them. It was really cute.
This morning, I noticed that the not so amazing, but still very nice, Carl was out working in their yard. I ambled down the street and struck up a conversation with him. We discussed what he was doing, the work I need to do on my roses, how nice their deck looks with the plant racks by the hot tub. He was telling me that he thinks the steam from the hot tub really helps the plants when he suddenly got it.
He stopped talking, looked at his deck, looked up at my house and blushed. I told him that in the future, when I saw the tub lights on that I’d smoke on my front deck. He asked if he could come up and look off my back deck and I agreed. He called in the door to the amazing Carl and they both came up to my place. When the amazing Carl looked down at their deck from mine, he blushed as well.
They are doing something with shade cloth and 2X4s now. I’m guessing that the “neighbor’s with benefits” thing is going away. Once they are finished, I’ll invite them back up to look down at their work.
Just to add to the fun, my crazy neighbor came out to give us the glare of death and they both smiled and waved at her and wished her a wonderful day. She went inside and slammed the door.
Oh, so you let them in on that too?
Nicely done, flatlined! 
You go, girlfriend! <said with a finger snap / wave> 
I hate it when a story ends and I still am totally confused as to the plot or the characters.
I thought that was normal when the plot centres around naked people?
Am I a bad person in that, if there were attractive ladies having naked hot tub time and I could see, I wouldn’t tell a damn soul?
Nice 
But I still dont understand why is there a Carl couple. I still cant figure out if flatlined was talking about a gay couple all along, or a straight one but with several men in it.
I assume a gay couple, as in the OP she refers to “one of the men” and has only referred to two people at all in the (very entertaining) story.
The definition of “traditional couple” has shifted a lot then.
Yes, that threw me for a bit of a loop, but contextually, gay couple made most sense. Traditional may mean here not nudists or exhibitionists etc.