Yeah you're 100% right, theres a purpose as to why their is 7 of them,
In 1129, their was the catholic military order also known as the knights templar or the order's of solomon's templar, they were humble, polite and helped people,and were sooo rich they were able to make some.sort of an army, they build a church , but inside that church they used to practice whichtcraft and other disgusting shit, after years they got caught, some of them run away to scotland.
The interesting.part is that the knights templar started at first with 7 members, and also they were the one who created the free masonary, and started building lodges for their secret reunion, and gothic churches, were they used to decorate them with spells, phrases that praise satan, and their only god, those churches were used as portals to the underground where they could practice whichcraft, freely. Thats why, they have geomatry as a very valuable word, and that why they called themselves the free masons.
Now i believe that bts are portraying those 7 members named knights templar. Also the number 7 is a very important number in a lot of religions . Something related to energies as well.
They portray also the 7 deadly sins, if you look close at eachone of them ull realise it.