u/Rustyspottedcats

The Seven (The Boys)- They only have the full seven members at the start of Season 1 and briefly during Season 3. More often, they have around five or six members, though the identity of said members fluctuates quite a bit.

Organization XIII (Kingdom Hearts)- They start off with six members, spend several years acquiring the remaining seven to get to thirteen, then get a fourteenth (Xion) and promptly lose five at Castle Oblivion. All in all, they have 13 members for about a week.

The Three Musketeers (The Three Musketeers)- They start off with three, but once d'Artagnan joins, they have four. They're also rarely depicted using muskets despite being called "musketeers", but that's neither here nor there.

Maroon 5 (Real Life)- They currently have six members.