May you have peace!
The 144,000 are PART of the group that makes up the nation of king and priests to the Most Holy One of Israel, JAH of Armies. They are taken, literally, from "among the sons of Israel"... from all of the tribes except Dan (Joseph, the penultimate son of Jacob (Israel), receives two shares.) They are chosen... and "sealed"... because of God's promise to Abraham regarding his (Abraham's) seed: Abraham was promised that his seed (descendants)... through his son, Isaac... would be a chosen people for God.
Initially, the nation of Israel was to be that nation of kings and priests to God. This began to change when they rejected God as their king and asked for a human king. They were initially given Saul and told that the consequence of having such a king (a human) was that he would dominate them. After Saul, they were given other kings, until finally, the king that God had chosen for them (whom they couldn't wait for), appeared. He, too, they rejected and, as a result, God rejected them... as His Holy nation... and opened the way for people of the "nations" - non-Israelites... to be apart of that nation of kings and priests. To ensure that His promise to Abraham did not go unfulfilled, however, He reserved 144,000 slots in that nation... for those from among Abraham's seed.
The other part of that nation (of kings and priests) consists of a great crowd of folks from ALL nations, tribes, tongues and people... including more from Israel. Together, these (the 144,000)... AND the great crowd... enter into the spirit realm, so as to stand BEFORE the throne of God... and render sacred Him sacred service... in His "temple."
This not quite the same as the "little flock" and "other sheep" -
The "little flock" is made up of Jews ONLY... which are those of only two (2) tribes of Israel, Judah and Benjamin. Many scholars teach that the word "Jews" included the other tribes, so that ALL Israelites are "Jews." They base this on the misstatements that when the Jews, who were exiled in Babylon left and returned to Jerusalem, all of the Israelite tribes were included. That is false: the 10-tribe kingdom of Israel (which excluded Judah and Benjamin) were not IN Babylon; they had been exiled to Assyria and was still there when Jeremiah wrote of the exile of the Jews into Babylon. They (the 10-tribe)... are referred to as "Samaritans" (based on where they were taken, Samaria).
Thus, the "little flock" are Jews (those of the 2-tribe kingdom of Judah/Benjamin)... and the "other sheep" are all those called who are NOT Jews (i.e., those of the "nations") and includes those of the 10-tribe kingdom of Israel. Cornelius was of this latter group: a Samaritan (of the 10-tribe kingdom), and thus second in line, after the Jews.
In contrast, the "144,000" are made up of Judah and Benjamin (Jews)... AND nine of the other 10 tribes (Samaritans)... and the "great crowd" is made up of people of ALL nations... as well as of Israel, both Jews AND Samaritans:
Jews Samaritans Non-Israelite Nations
Little Flock Other Sheep Other Sheep
144,000 144,000 Great Crowd
Great Crowd Great Crowd
As for whether there are any of the 144,000 in the WTBTS, the answer is, no. First, they would only be such if they are direct descendants of Abraham. Second, even if that were the case, they would not be among ANY of these groups... if they are still connected/loyal to that organization... or any human organization. True, they may be CALLED... which is what their experience most likely is... but they are not CHOSEN... until the QUIT "touching the unclean thing." Many are called... few... are chosen.
That is why the reference to the 144,000 being "virgins" - it is not that they never had sex with a literal woman. It is that they have been washed clean in the blood of the Lamb, so that they become "undefiled,"... and they remain "undefiled" by not "touching" any woman... any RELIGION... which women are "the daughters" of Babylon the Great.
Babylon the Great... is a harlot... in that she had a husbandly-owner, but chose to commit fornication with the kings of the earth. As a result, she had "children"... daughters... "christians" religions. BTG... consists of those ANOINTED... who claim to belong to Christ (their "husbandly owner")... but "adulterate" that relationship by their relationship with "earthly" kings (i.e., governments, religions, institutions, agendas, politics, purposes, etc.). Rather than remain faithful to their ONE husband... by means of remaining faithful to HIS laws... they take on the "laws" of another/others... and so became faithful to them. Adultery.
Her "daughters"... the religions that have come out of her... are guilty of the same things, so that she (BTG) is also called "the MOTHER of the harlots."
But those who are considered "virgins"... are those who remain faithful to Christ... by remaining in the law of HIS "house"... and so have NO "relations" with ANY other "husband(s)."
There are some who believe that ancient Israel (Oholah and Oholibah) are the same as BTG. This is incorrect, however, because while it is true that Israel "committed adultery" against the Most Holy One of Israel... by going off after other gods, BTG commits fornication against Christ, the Son. Like Israel, therefore, she is replaced... by New Jerusalem... the "bride" of Christ... those who do NOT "fornicate"... with ANYONE else... but follow, listen to... and obey... only One. Their husbandly-owner, the One who bought them with HIS blood... Christ. And no other.
I hope this helps, and I bid you peace.
Your servant and a slave of Christ,
SA