There seems to be a lot of confusion and sometimes purposeful
misleading regarding what France means when he calls himself a “Big Brother.”

On one hand, you have people who have only watched the dub,
haven’t read a page of the manga, and worst of all, incorrectly declare that
France is related to all the nations who either call him big brother, or who he
claims to be the big brother of. There’s also people who know this is false,
but still use the misunderstanding as a way to immaturely elevate their own
ship and degrade shippers of the opposite kind.

To that, I say this: the dub is never canon. I totally get why
there’s a lot of misconceptions regarding the family tree, though. For example,
in the dub, Switzerland is referred to as France’s relative, meanwhile, in the
strip material, Switzerland is listed as France’s neighbor.

Again, don’t ever use the dub as a source. It’s like the
Wikipedia equivalent of canon material; it gives you a general idea, but in no
way is it totally correct. While I understand how limited the anime medium can
be in portraying all canon information, it’s still your responsibility to do
your research. 

That said, if you’ve read the manga, you would know that France
doesn’t have any siblings. That’s right. He’s not a big brother at all, but
rather, he’s listed as a big brother type. Likewise, he’s also referred to
himself as “the Big Brother of the world.”

In other words, because France is self-conscious of his age, he
opts to be a big brother mentor figure as opposed to identifying as an elder.
Although, admittedly, he has occasionally adopted a parental role. This is
especially the case with America, whom France expresses disdain at England for
raising so poorly.

Regardless, the following few strips demonstrate how France will
claim to be the big brother of literally anything.

Here, he deems himself to be the big brother of the reader. No,
I’m not kidding.

When he meets Lisa, Jeanne d’Arc’s reincarnate, he introduces
himself as “Big Brother France.”

The rest is pretty straightforward. Aside from the explicit
character description, there’s no possible way he would be related to them all
without it creating the need for other nations to be related to each other.

England:

Italy:

Germany:

Seychelles:

In sum, “Big Brother France” is not actually a big brother.

He’s a big brother figure.