I can´t say that it´s wrong, but 1. "ihnen" is in german like "they" so you asked "How are they?".
Nope. "Ihnen" can be "
them or you".
2. "ihnen" can be singular when it´s in a polite form ( when you are speaking with teachers or old people)
That's correct. You use it to unknown persons or persons of higher rank.
The German polite form has the exactly same grammar forms as the 3. plural form. English and French people use the 2. plural form as the polite pronoun! (Only in medieval German we also use the German 2. plural form for polite speaking. Which is not what you should do.)
It's quite easy. If it is the polite singular form it is a personal pronoun, if it is the plural form it is a
possessive pronoun dativ form.
example:
a.) Ich habe zwei Brüder. Das Haus gehört ihnen. - I have two brothers. The house belongs to them.
(they are possessing something! (possessive pronoun))
edit: Michel is right. It is not a possessiv pronoun (which would be: 'Es ist ihr Haus/The house is theirs') but a dativ form.
b.) Hallo Herr Müller. Wie geht es Ihnen? - Hello Mister Müller. How are you? ("Ihnen" = Herr Müller (
personal pronoun); also note that in this case Ihnen has a capital I in the beginning)
Singular:
Ich gehe - I go
Du gehst - you go
er/sie/es geht - he/she/it goes
Plural:
wir gehen - we go
ihr geht -
you gosie gehen - they go
The blue market forms are also the
polite forms when talking to one person. In which case you would also write the German "Sie gehen" with a capital first letter. Like with the example above.
There's also one Impersonal 3rd singular person:
man geht - you go/one goes
in English the impersonal singular form can be 3rd or 2nd singular person.
But to be honest.
READ READ READ and you will get a feeling about when to use what noun.
edit: this might also help you.
http://de.wikipedia.org/wiki/Personalpronomen
http://de.wikipedia.org/wiki/Possessivpronomen