By a strange coincidence we had a very similar English-Spanish question only last week. The terms were pipes, ranks and stops, and my answer was tubos, hileras y registros:
http://www.proz.com/kudoz/english_to_spanish/music/6195925-p...

Well, let me start with hileras, and borrow some of what I said there. An hilera is a row of pipes, one for each note on the keyboard:

"Hileras: Cada una de las filas de tubos que componen un juego o registro completo."
http://www.organosdepalencia.com/glosario.html

In English it's called a rank:

" Rank
A rank is a row of pipes. The row always has all pipes of the same kind of sound. For example, all the pipes for a Spitzflute (one kind of flute sound) will be in the same row."
http://nersp.nerdc.ufl.edu/~bodinew/Pages/Glossary.html#R

"RANKS: Rows of pipes graduated in length, one per key, corresponding to the entire compass of the keyboard."
http://wicksorgan.com/display_page?p=290

Now, a stop, which is "an individual voice in the organ" (such as a particular flute sound) is "composed of one or more ranks of pipes". In other words, with most stops, when you play a note, one pipe sounds, but with some stops, called mixtures, more than one pipe sounds. Each of these sets of pipes is called a rank:

"An organ stop (or just stop) is a component of a pipe organ that admits pressurized air (known as wind) to a set of organ pipes [...]
Certain stops called mixtures contain multiple ranks of pipes sounding at consecutive octaves and fifths (and in some cases, thirds) above unison pitch. The number of ranks in a mixture is denoted by a Roman numeral on the stop knob; for example, a stop labeled "Mixture V" would contain five pipes for every note. So, for every key pressed, five different pipes sound (all controlled by the same stop)."
https://en.wikipedia.org/wiki/Organ_stop

Similarly, in Spanish, one "registro" (stop) may control one or more "hileras":

"Las Mixturas, (Lleno, Compuestas, Címbala, Cimbalillo, Cimbalete, Corona, Fornitura...), son varias hileras de tubos por punto (tecla) que cantan coincidentemente. [...] El Corneta es un juego de una riqueza armónica extraordinaria, que inicia en el Sol2 , en el Do3, o en el Do#3. Consta de varias hileras de tubos por punto."
http://filomusica.com/filo15/modest.html

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Now for juegos. In the previous question, this was proposed for "ranks", and the meaning is really very similar. Juego means the set of pipes associated with one stop:

"Juego: Gama completa de tubos pertenecientes a una misma familia y entonación que abarca la extensión completa del teclado."
http://www.organosdepalencia.com/glosario.html#j

This means that the meaning of juego and registro (stop) is very similar, and in some contexts they are synonymous.

Now, for stops with one rank, the "juego" is, in effect, a rank. But a juego can consist of more than one rank. There are "juegos simples" and "juegos compuestos":
https://books.google.es/books?id=XYgGBAAAQBAJ&pg=PA36#v=onep...

"Órdenes compuestos. Juegos. registros múltiples, de varias hileras"
Órdenes simples. Juegos, registros de una sola hilera."
https://books.google.es/books?id=0sHWhJItAj0C&pg=PA333&lpg=P...

The word for "juego" in English is actually "register":

"REGISTER: Register is another word for the complete set of pipes — one rank or multiple ranks — that makes up one stop. That is, register is another word for stop. "
http://www.npr.org/2006/06/05/5448985/organ-music-pulling-ou...

"The term [stop] is also sometimes used as a synonym for register, referring to rank(s) of pipes controlled by a single stop."
https://en.wikipedia.org/wiki/Organ_stop

(I'll add another couple of references shortly)

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Note added at 6 hrs (2016-09-30 20:34:15 GMT)
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I just wanted to add that in Spanish you can have stops that are "medio juego", as in this example:

"60 registros: 48 juegos enteros, 5 medios juegos, 5 acoplamientos, 2 trémolos, 3030 tubos."
http://www.santuariodecovadonga.com/subnivel2/organo.htm

(As I explained in the previous question, acoplamientos or couplers are stops that link manuals, so that when you play one another sounds as well, and a tremolo is as an effect that produces a fluctuating sound by varying the air flow.)

Well, medios juegos are half registers, meaning that there is not a full set of pipes for every note on the keyboard but only for half, usually the upper half. See the specifications for certain stops on this organ in Navarra:

"Stop List
[...]
Flauta Basca - 4 - Half-register, right hand only
Ocarina - 4 - Half-register"
And so on
http://iof.pipechat.org/getpdf.php?file=03403100014