Evo ukratko:

članak 15 princip
1) svaki igrač koji ima trajno državljanstvo može igrati za reprezentaciju te zemlje
2) s iznimkom uvjeta navedenim u članku 18 svaki igrač koji je sudjelovao u utakmici službenog natjecanja bilo koje kategorije i vrste za neku zemlju, ne može igrati za reprezentaciju druge zemlje

to je dakle osnovni princip.

Članak 16 se dalje odnosi na zahtjeve za igrače koji udovoljavaju uvjetima članka 15 i mogu igrati za više reprezentacija, jer imaju više državljanstava (gdje je pod b da mu se je barem 1 roditelj rodio u državi za koju želi nastupat).
Alen Halilović ne ispunjava stavak 2) članka 15 jer je igrao za Hrvatske mlade reprezentacije. Dakle, ako želi nastupati za bilo koju reprezentaciju osim Hrvatske mora ispuniti uvjete iz članka 18 koji kaže

članak 18 promjena saveza

1)Ako igrač ima više državljanstava može do svog 21 rođendana promjenu da nastupa za drugu zemlju pod sljedećim uvjetima:
a) da nije igrao utakmicu službenog natjecanja za A vrstu zemlje za koju trenutno nastupa i da je u vrijeme svog prvog reprezentativnog nastupa u službenom natjecanju za reprezentaciju stare zemlje već imao državljanstvo nove zemlje za koju želi nastupati, što A. H. nema

Dakle, prema ovome Alen Halilović ne može nastupati za Bih, samo za RH
Samir je očito bio pozivan u mlađe brazilske kategorije ali izgleda nije zabilježen nijedan nastup u službenom natjecanju

evo i kompletnog pravila Fife što se tiče mijenjanja nogometnog državljanstva

VII. ELIGIBILITY TO PLAY FOR ASSOCIATION TEAMS

Article 15 Principle

1 Any person holding a permanent nationality that is not dependent

on residence in a certain country is eligible to play for the

representative teams of the Association of that country.

2 With the exception of the conditions specified in article 18 below, any

Player who has already participated in a match (either in full or in

part) in an official competition of any category or any type of football

for one Association may not play an international match for a

representative team of another Association.

 

Article 16 Nationality entitling playersto represent more than one Association

1 A Player who, under the terms of art. 15, is eligible to represent

more than one Association on account of his nationality, may play

in an international match for one of these Associations only if, in

addition to having the relevant nationality, he fulfils at least one of

the following conditions:

(a) He was born on the territory of the relevant Association;

(b) His biological mother or biological father was born on the

territory of the relevant Association;

(c) His grandmother or grandfather was born on the territory of the

relevant Association;

(d) He has lived continuously on the territory of the relevant

Association for at least two years.

2 Regardless of par. 1 above, Associations sharing a common nationality

may make an agreement under which item (d) of par. 1 of this article

is deleted completely or amended to specify a longer time limit. Such

agreements shall be lodged with and approved by the Executive

Committee.

 

Article 17 Acquisition of a new nationality

Any Player who refers to art. 15 par. 1 to assume a new nationality

and who has not played international football in accordance with art.

15 par. 2 shall be eligible to play for the new representative team

only if he fulfils one of the following conditions:

(a) He was born on the territory of the relevant Association;

(b) His biological mother or biological father was born on the

territory of the relevant Association;

(c) His grandmother or grandfather was born on the territory of the

relevant Association;

(d) He has lived continuously for at least five years after reaching the

age of 18 on the territory of the relevant Association.

 

Article 18 Change of Association

1 If a Player has more than one nationality, or if a Player acquires a new

nationality, or if a Player is eligible to play for several representative

teams due to nationality, he may, up to his 21

st

birthday, and only

once, request to change the Association for which he is eligible to

play international matches to the Association of another country of

which he holds nationality, subject to the following conditions:

(a) He has not played a match (either in full or in part) in an official

competition at “A” international level for his current Association,

and at the time of his first full or partial appearance in an

international match in an official competition for his current

Association, he already had the nationality of the representative

team for which he wishes to play.

(b) He is not permitted to play for his new Association in any

competition in which he has already played for his previous

Association.

2 If a Player who has been fielded by his Association in an

international match in accordance with art. 15 par. 2 permanently

loses the nationality of that country without his consent or against

his will due to a decision by a government authority, he may

request permission to play for another Association whose

nationality he already has or has acquired.

3 Any Player who has the right to change Associations in accordance

with par. 1 and 2 above shall submit a written, substantiated request

to the FIFA general secretariat. The Players’ Status Committee shall

decide on the request. The procedure will be in accordance with the

Rules Governing the Procedures of the Players’ Status Committee

and the Dispute Resolution Chamber. Once the Player has filed his

request, he is not eligible to play for any representative team until his

request has been processed.