I'll just seize on one point here.
NicholasMarks apparently believes in the Planet X/Nibiru bullshit. Since he's also a young-earth creationist, that puts him solidly in the running for the title of the dumbest human being presently alive on the planet Earth.
Planet X lunatics apparently live in a world where literally no one owns a powerful telescope except a few astronomers at universities or even knows what the fucking night sky looks like at any given time of the year, a skill our primitive ancestors had ten thousand years or more ago. Also, in their world, government is this incredibly effective, efficient monolith capable of silencing nearly anyone and everyone before De Truth Gets Out.
A low-mass M-dwarf either in orbit around the sun or on a path that would take it INTO the inner solar system would be very, very detectable many, MANY years before it finally got anywhere near the inner solar system--where "inner" is defined as "anything closer than the Kuiper Belt. And I don't mean just to professional astronomers on government payrolls, I mean to the hundreds of thousands of amateur astronomers with decent telescopes around the world. And if it goes close enough, long before it crossed Neptune's orbit, it would be visible to the naked eye as something moving noticeably across the sky. Because it's a goddamn fully-fusing star.
A brown dwarf--defined as a substellar object ~13 times massive than Jupiter and able to fuse deuterium in its core for a limit time early in its youth--might be slightly harder to detect, but it too should be relatively trivial to detect by amateurs if it were that close as well. All it would take is one--ONE--whisper about it, and within a day, half a million telescopes would be trained on that spot.
An actual PLANET--even one less massive than Earth--should be visible as a moving object in the sky a long distance away, and it would be spotted by amateur astronomers long before it became a naked-eye object.
The only way around these assumptions would be that the damned thing is invisible and/or being artificially propelled at unnatural speeds. Since you're supposedly convinced it was spotted by the IRAS survey in the 1980s, it's obviously visible, so either it cloaked recently, or your assumptions fall completely apart. Without actual, irrefutable proof that it both exists AND that it somehow cloaked like a Klingon Bird of Prey, I'm going to assume you're both barking mad and fucking stupid to boot. Even if it WAS invisible to the naked eye now, it should have a gravitational influence that would have shown up by this point--and yes, the perturbations it would inflict on the other planets of this solar system would ALSO be detectable by backyard amateur astronomers all over the world. Unless the gravitational effects are somehow being cloaked, too--in which case, since it has no objective verifiable existence or noticeable effect on anything in this solar system, why be afraid of it at all?
Planet X lunatics apparently don't realize that (1) scientists are shit at keeping secrets even with government orders, (2) there's a metric fuckton of them and they're all over the world,(3) any conspiracy to keep them all quiet would fall apart before it ever get out of the board meeting because trying to get a plurality of national governments to agree on ANYTHING is like herding cats, and (4) people have fucking eyes of their own, talk to each other, and can build telescopes and other scientific equipment out of off-the-shelf parts that's leagues better than most of the gear used by scientists in the 1950s, and they fucking notice things.
