Jeśli nadal będziesz kaszleć i kichać jutro rano, zostań w domu.

That is a normal difference between Polish and English.

In Polish, when the condition is about the future, it is very common to use the future tense after jeśli:

• Jeśli będziesz kaszleć... = If you are still coughing / if you still cough...

English usually avoids will after if, but Polish does not have that restriction in the same way. So Jeśli będziesz... is completely natural.

Because this is the standard future construction for imperfective verbs in Polish.

Both kaszleć (to cough) and kichać (to sneeze) are imperfective, so their future is made with:

• będę / będziesz / będzie...
  • infinitive

So:

• będziesz kaszleć = you will be coughing / you will cough
• będziesz kichać = you will be sneezing / you will sneeze

The conjugated part is będziesz. The main verbs stay in the infinitive.

Because one auxiliary can apply to both infinitives:

• będziesz kaszleć i kichać

This is like saying you will cough and sneeze in English. You do not need to repeat will, and Polish does not need to repeat będziesz either.

You could repeat it for emphasis, but normally you would not:

• będziesz kaszleć i kichać — natural
• będziesz kaszleć i będziesz kichać — grammatical, but heavier and less natural here

Nadal means still.

So:

• Jeśli nadal będziesz kaszleć... = If you are still coughing...

You could also use wciąż here:

• Jeśli wciąż będziesz kaszleć...

That sounds natural too.

Dalej can also mean still in some contexts, especially in speech, but nadal is a very safe and neutral choice here.

Yes. Polish word order is flexible.

This sentence has:

• Jeśli nadal będziesz kaszleć i kichać jutro rano, zostań w domu.

But you could also say:

• Jeśli jutro rano nadal będziesz kaszleć i kichać, zostań w domu.
• Jeśli będziesz jutro rano nadal kaszleć i kichać, zostań w domu.

These all mean basically the same thing. The difference is mostly emphasis and rhythm, not core meaning.

Zostań is the imperative form of zostać.

Here it means:

• stay
• remain

So:

• zostań w domu = stay at home

Polish often uses a perfective imperative for a single, concrete instruction like this. That is why zostań sounds natural.

Zostawaj would be the imperfective imperative, and it would sound more like:

• keep staying
• stay repeatedly / as a habit

That does not fit this situation as well.

One more important note: zostać can also mean become in other sentences, but here, with w domu, it clearly means stay/remain.

Because w domu expresses location, not movement.

• w domu = in/at home
• do domu = to home / to the house (direction toward home)

Since the sentence says stay at home, Polish uses w:

• zostań w domu

If the meaning were go home, then you would use do domu:

• Idź do domu. = Go home.

It is the locative singular of dom.

The preposition w often takes the locative when it means in or at:

• dom → w domu

So:

• w domu = in/at home

This is a very common phrase, so it is worth memorizing as a chunk.

Because Polish usually drops subject pronouns when they are not needed.

The verb forms already show who the subject is:

• będziesz = you will (singular, informal)
• zostań = stay! (to one person, informal)

So ty is unnecessary.

You could add ty for emphasis or contrast, but normally Polish leaves it out.

Yes. It is addressed to one person in the informal form.

You can tell from:

• będziesz
• zostań

These are forms used with ty.

A formal version would be something like:

• Jeśli nadal będzie pan/pani kaszleć i kichać jutro rano, proszę zostać w domu.

A plural informal version would be:

• Jeśli nadal będziecie kaszleć i kichać jutro rano, zostańcie w domu.

Because Jeśli nadal będziesz kaszleć i kichać jutro rano is a subordinate clause introduced by jeśli.

In Polish, clauses introduced by jeśli are separated by a comma:

• Jeśli..., zostań...

This is standard Polish punctuation.

Yes, depending on context.

Because they are imperfective, they often express an ongoing or repeated action. In English, that can come out as:

• cough / sneeze
• be coughing / be sneezing

So będziesz kaszleć i kichać could feel like:

• you will cough and sneeze
• you will still be coughing and sneezing

In this sentence, because of nadal and the health context, the English idea is often closer to still be coughing and sneezing.

It is the most straightforward and neutral choice here.

Jeśli is the standard word for a real condition:

• Jeśli będziesz chory, zostań w domu.
• If you are sick, stay home.

Another common word is gdyby, but that usually introduces a more hypothetical or less real situation, often like if ... were / if ... should.

So for this sentence, jeśli is exactly the right choice.