Ihr liegt bei der Stichfrage richtig.

Here Ihr means you (plural), as in you all.

A few things can confuse learners:

• ihr can also mean her in the dative case.
• At the start of a sentence, German capitalizes the first word, so Ihr here does not automatically mean formal address.
• Modern formal you is Sie, and it would take liegen, not liegt:
  Sie liegen ...

So in this sentence, Ihr liegt clearly means you (plural) are / you (plural) lie in grammatical terms.

The infinitive is liegen.

Its present-tense forms are:

• ich liege
• du liegst
• er/sie/es liegt
• wir liegen
• ihr liegt
• sie/Sie liegen

So ihr liegt is the normal 2nd person plural form.

The confusing part is that liegt is also the 3rd person singular form, but because the subject is ihr, here it must be 2nd person plural.

No. This is an idiomatic use.

While liegen often literally means to lie or to be lying down, German also uses it in expressions like:

• richtig liegen = to be right
• falsch liegen = to be wrong
• gar nicht so falsch liegen = not be that far off

So Ihr liegt ... richtig means you are right / correct, not you are lying down correctly.

Richtig liegen means to be correct, to be right, or to have guessed/judged correctly.

It is especially common when talking about:

• guesses
• estimates
• answers
• judgments
• assumptions

For example:

• Du liegst richtig. = You’re right.
• Ihr liegt falsch. = You’re wrong.

So in your sentence, it means that you got it right with respect to the Stichfrage.

Bei der Stichfrage means something like:

• on the tie-breaker question
• with the tie-breaker question
• when it comes to the tie-breaker question

The preposition bei takes the dative case, which is why die Stichfrage becomes der Stichfrage.

So:

• nominative: die Stichfrage
• dative after bei: bei der Stichfrage

Here bei is not really about physical location. It is being used in a more abstract sense: in relation to or regarding the tie-breaker question.

A Stichfrage is a tie-breaker question or deciding question.

It is commonly used in:

• quizzes
• contests
• game shows
• competitions

If two participants are otherwise tied, the Stichfrage decides the winner.

So the sentence is saying that you are correct on the tie-breaker question.

Because richtig belongs with liegt as part of the expression richtig liegen.

German main clauses usually place the conjugated verb in the second position, and other sentence elements can come after that. In this sentence:

• Ihr = first element
• liegt = second-position verb
• bei der Stichfrage = prepositional phrase
• richtig = complement to liegt

So the structure is normal and natural.

You will often see this pattern:

• Du liegst richtig.
• Ihr liegt bei der Antwort richtig.
• Sie liegen damit falsch.

It is understandable, but Ihr liegt ... richtig is the more idiomatic expression here.

German strongly prefers:

• richtig liegen
• falsch liegen

If you want alternatives, more natural ones would be:

• Ihr habt bei der Stichfrage recht.
• Ihr habt die Stichfrage richtig beantwortet.

So Ihr seid ... richtig is not the best choice in this context.

It is talking to more than one person.

The subject ihr is the normal informal plural you. English used to have ye/you all distinctions historically, but modern standard English usually just says you for both singular and plural, so German is more specific here.

So this sentence addresses a group:

• ihr = you all / you guys / you two / you people

If it were singular informal, it would be:

• Du liegst bei der Stichfrage richtig.

If it were formal, it would be:

• Sie liegen bei der Stichfrage richtig.