"Are you her brother?"

Translation: Jesteś jej bratem?

[smaevska]

Why Jesteś , not Jestesz ?

[immery]

być is exception.

[mihxal]

Because this word has such a form and not different.

[MarkBennett6]

...because life's a być?

[Pete357534]

When does one use "czy?"

[Jellei]

When you ask a Yes/No question.

"Czy" is optional, though. It could be used here, but as you see, it was not.

[Pete357534]

Thanks!

[stephan1111]

Why is it jej? Shouldn't it be the instrumental case of the third person singular (feminine) pronoun ona (so it should be nią?) Since bratem is in the instrumental case, shouldn't the case of the pronoun also agree?

Or is it an exception since jej is a possessive pronoun (so it's always the genitive case)?

[Jellei]

Possessive pronouns for 1st and 2nd person undergo declension, but those for 3rd person always have just one form. So "her" as in "her dog" or "her brother" will always be "jej", no matter of the case the whole noun phrase will be using.

[Sdotwebb]

What is the difference from Brat vs Bratem?

[Jellei]

Cases.

"brat" is the basic, Nominative form.

"bratem" is Instrumental. It is mostly needed in sentences like "He is her brother" and also when something happens "with her brother".

[dlk08508]

You wouldn't happen to have a website that shows like...a grid of the tenses and when to use them would you?

[alik1989]

Did you mean cases instad of tenses? If so, use wiktionary for declension tables and check out this site which explains most of the applications of each case and shows you the most common declension patterns.

[Adam164490]

Czy pan jest jej bratem?

[Jellei]

Sure, added now.

[motownread]

Is "Jesteś bratem jej" acceptible?

[Jellei]

No, that sounds super weird.

[Nik659150]

Why bratem and not brat ?

[Jellei]

"jesteś" takes a noun phrase in Instrumental.

[Kim921666]

Why can I not use jesteście as I cannot tell how many you is referring to?

[alik1989]

Then it would have been 'brothers', wouldn't it?

[Kim921666]

Yes it would thank you.

[Ryszard386408]

What about "Czy jesteście jej bratem?"

[Jellei]

Unlike Russian of French, Polish "jesteście" is undoubtedly 2nd person plural, it cannot be a way of referring to one person in a formal way. So your question is "Hey, you two! Are you her (one) brother?", which is of course ungrammatical.