Jeżeli dostaniemy awans, będziemy mieli więcej obowiązków, ale też większą pensję.

Yes. Jeżeli and jeśli both mean if.

In this sentence, Jeżeli sounds a little more formal or careful, while jeśli is very common in everyday speech. So all of these are natural:

• Jeżeli dostaniemy awans...
• Jeśli dostaniemy awans...

The meaning is the same here.

That is because dostać is a perfective verb.

In Polish, perfective verbs do not normally have a true present tense. Their present-looking forms are used to talk about the future. So:

• dostanę = I will get
• dostaniesz = you will get
• dostaniemy = we will get

So Jeżeli dostaniemy awans means If we get a promotion.

That is a very common question for English speakers.

Polish works differently from English here. In Polish, when you are talking about a real future possibility, it is normal to use future meaning in both parts:

• Jeżeli dostaniemy awans, będziemy mieli...

Literally, both verbs point to the future.

So even though English says:

• If we get a promotion, we will have...

Polish naturally says:

• If we will-get a promotion, we will have...

This is normal Polish grammar, not a mistake.

Awans is in the accusative singular, because it is the direct object of dostaniemy.

The verb dostać usually takes an object in the accusative:

• dostać prezent = to get a present
• dostać pracę = to get a job
• dostać awans = to get a promotion

Here, awans is a masculine inanimate noun, and in the singular its accusative form is the same as its nominative form, so it looks unchanged.

Both are possible.

Polish can form the future of an imperfective verb like mieć in two main ways:

• będziemy mieli
• będziemy mieć

Both mean we will have.

The version in your sentence, będziemy mieli, uses the compound future with the past-form element mieli. This part agrees with the subject:

• będziemy mieli = if the group is male or mixed
• będziemy miały = if the group is all female

So if a group of women said this sentence, it would be:

• Jeżeli dostaniemy awans, będziemy miały więcej obowiązków...

Because mieli is the plural form used for a group that includes at least one male, or for a mixed/unspecified group.

Polish past-type forms and this kind of future form show grammatical gender in the plural:

• my byliśmy / będziemy mieli for masculine-personal groups
• my byłyśmy / będziemy miały for all-female groups

So będziemy mieli tells you that the speakers are either:

• a mixed group,
• a group of men,
• or just a general we where masculine-personal is used as the default.

Because they express more in two different ways.

więcej means more in the sense of a greater quantity or number.

• więcej obowiązków = more duties / more responsibilities

But większą comes from większy, meaning bigger / greater as an adjective that agrees with the noun:

• większa pensja = a bigger salary

So:

• więcej obowiązków = more responsibilities
• większą pensję = a bigger salary

That is why the forms are different.

Also, with salary, Polish often uses wyższa pensja meaning higher salary, which may sound even more natural in some contexts. But większa pensja is understandable and acceptable.

Because więcej is followed by the genitive.

The basic forms are:

• obowiązek = duty / obligation
• obowiązki = duties / obligations
• obowiązków = of duties / duties after words like więcej

So:

• więcej obowiązków = more duties

This is a very important pattern in Polish. After words like więcej, mniej, dużo, mało, you often get the genitive:

• więcej czasu = more time
• mniej problemów = fewer problems
• dużo pracy = a lot of work

Because pensję is the accusative singular form, and it is the direct object of będziemy mieli.

The noun is:

• pensja = salary

But after mieć, you need the accusative:

• mieć pensję = to have a salary

So:

• nominative: pensja
• accusative: pensję

This change is typical for many feminine nouns ending in -a.

Też means also or too.

So:

• ale też większą pensję = but also a bigger salary

It adds the idea that there is a positive side as well. We will have more responsibilities, but also a bigger salary.

You could also say:

• ale także większą pensję

That is very similar, though także can sound a little more formal.

Not completely. Polish word order is fairly flexible, but the original order is very natural:

• Jeżeli dostaniemy awans, będziemy mieli więcej obowiązków, ale też większą pensję.

This order gives a clear contrast:

• negative or heavier side: więcej obowiązków
• positive side: ale też większą pensję

You can move words around in Polish, but that often changes emphasis rather than basic meaning. For a learner, the original word order is a very good model to follow.

Because Polish usually does not need subject pronouns when the verb ending already shows who the subject is.

Here the verbs tell you it is we:

• dostaniemy = we will get
• będziemy = we will be / we will
• mieli = had, here part of we will have

So adding my is possible, but not necessary:

• Jeżeli dostaniemy awans... = normal
• Jeżeli my dostaniemy awans... = possible, but more emphatic

Usually Polish leaves my out unless you want contrast or emphasis.