As AudeSapere said, if Jehovah's Witnesses accepted the Catholic Church to be the one true institution of God, they'd be Catholics.
Historically, Jehovah's Witnesses are a Protestant Adventist religion, descending (and you can take that any way you want to) from the Baptist Millerite movement (see Wikipedia http://en.wikipedia.org/wiki/William_Miller_(preacher)) of the 1830s.
Adventist religions are typically apocalyptic, and when William Miller's apocalypse didn't come, Charles Taze Russel took his turn at bat after some coaching from George Storrs and a couple of other post-Millerite apocalyptic. The Seventh-Day Adventists also sprang from this lot, but they were clever enough not to set a date for "the end."
Not so Russell. He felt that 1878 was the winning lotto number. Then he tried 1914. He died in 1916, never seeing the failure of his last selected date, 1918. Russell died on Halloween 1916 wearing his toga costume. (I kid you not!)
Russell was followed by the megalomaniac "Judge" Joseph Franklin Rutherford. When 1918 came and went, he pointed to the year 1925, saying it was a date "more sure than 1914," which is probably one of the most honest statements he's ever made, since both are baseless, as the passage of time has shown. Rutherford was an abusive alcoholic and died of fectal cancer. He abandoned his wife when he ascended to the leadership of the WTB&TS and spent a lot of his time in a mansion in San Diego while his wife lived about 150 miles away. Fortunately, he was not lonely. In addition to the angels that kept him company he had a couple of girlfriends. When his dead body was found in the basement of the mansion, rats had been nibbling on him for a few days.
After Rutherford died in 1942, kingship passed to the two-headed Knorr/Franz creature. Actually Nathan Knorr and Fred Franz were two of Rutherford's favorite lackeys prior to his death. Knorr ran the "business" of selling "Bible-study aids" while Franz was in charge of speaking with angels and setting new dates for the end of the world. He was the genius behind the 1975 fiasco, and most of the organization fell in line with him until it didn't come true.
Both Knorr and Franz are now dead. Knorr died in 1977 and Franz died in 1992 after his supply of tanna-leaf tea ran out.
Today the Watchtower Bible and Tract Society is run by a misogynistic geriatric pedophile-protecting fuster-cluck they call the governing body. Not one member of this group has the charisma or powerful personality of any of the previous presidents.
I was raised as a JW after being born a Roman Catholic. Today I am an atheist. I believe there is no god, and no "spiritual realm" populated with any creatures of the sort described by theologians.