Брат шутит, что он ещё не достаточно щедрый, чтобы покупать еду для всего класса.

Russian has no articles, so there is no direct equivalent of a or the.

So Брат can mean:

• brother
• a brother
• the brother
• sometimes even my brother, if the context makes that clear

In a real conversation, Russian often relies on context where English would need an article or a possessive.

In the present tense, Russian usually omits the verb to be.

So:

• он щедрый = he is generous
• literally: he generous

That is completely normal Russian grammar.
If you put it into the past or future, a form of быть appears:

• он был щедрым = he was generous
• он будет щедрым = he will be generous

Шутит is the 3rd person singular present tense of шутить.

So it means:

• jokes
• is joking

Here it means something like Brother is joking / Brother jokes that...

The verb шутить is imperfective, which fits because this is not a single completed joke as an event; it is just describing what he is saying in a joking way.

Что here means that and introduces a subordinate clause.

So:

• Брат шутит, что... = Brother jokes that...

This is very common in Russian after verbs of speaking, thinking, knowing, and so on:

• Он говорит, что... = He says that...
• Я думаю, что... = I think that...

Because after что, Russian starts a new clause, and that clause normally needs its own subject.

So:

• Брат шутит, что он... = Brother jokes that he...

In normal speech, leaving out он here would usually sound incomplete.

There is a more compressed style where Russian can omit the pronoun, especially with a short-form adjective, for example:

• Брат шутит, что ещё недостаточно щедр, чтобы...

That sounds more literary or compact. For a learner, the version with он is easier and more straightforward.

Yes. In fact, many speakers would naturally say:

• ещё недостаточно щедрый

This means still not generous enough.

The version in your sentence, ещё не достаточно щедрый, is understandable, but it puts more emphasis on the negation, roughly:

• still not sufficiently generous
• not yet generous enough

A useful rule:

• недостаточно as one word usually means not enough / insufficiently
• не достаточно as two words is possible when the speaker is more clearly negating enough

So both can occur, but ещё недостаточно щедрый is often the more standard-looking everyday choice.

Because щедрый is describing он, and here it is part of the predicate:

• он ... щедрый = he is generous

With the omitted present-tense to be, Russian normally uses the nominative form of the adjective:

• masculine singular nominative: щедрый

It matches он, which is masculine singular.

Other forms would mean different things:

• щедрого = genitive/accusative masculine animate
• щедрым = instrumental masculine singular

Those would not fit this structure.

Yes.

You could say:

• Брат шутит, что он ещё недостаточно щедр, чтобы покупать еду для всего класса.

Here щедр is the short form of щедрый.

The difference is mostly stylistic:

• щедрый sounds more neutral and conversational
• щедр sounds a bit more compact, literary, or formal

Both are grammatical.

Here чтобы means something like in order to or, in this pattern, enough to.

Russian often uses this structure:

• достаточно + adjective/adverb + чтобы + infinitive

So:

• достаточно щедрый, чтобы покупать...
• generous enough to buy...

Because the subject is the same person, Russian uses the infinitive покупать.

Compare:

• Он достаточно богат, чтобы путешествовать. = He is rich enough to travel.

If the subject changed, Russian would usually use a finite verb instead:

• Он достаточно богат, чтобы его дети учились за границей. = He is rich enough for his children to study abroad.

Because покупать is imperfective, and here it expresses a general or repeated kind of action, not one single completed purchase.

So the meaning is:

• to buy food for the whole class as a general idea
• not to buy it once on one specific occasion

If you said купить, it would sound more like:

• to buy food for the whole class one time

So:

• покупать = habitual/general/process
• купить = one completed act

In this sentence, покупать fits better.

Because еду is the accusative singular of еда and it is the direct object of покупать.

Dictionary form:

• еда = food

Accusative singular:

• еду

So:

• покупать еду = to buy food

This is a very common pattern:

• читать книгу = to read a book
• покупать еду = to buy food

Для takes the genitive case, so:

• класс becomes класса

Also, весь becomes всего to agree with класса in case, number, and gender:

• весь класс = the whole class
• для всего класса = for the whole class

It is singular because the meaning is one entire class as a group, not several classes.

Compare:

• для всего класса = for the whole class
• для всех классов = for all the classes

Yes, that is possible.

You may also hear:

• покупать еду всему классу

This uses the dative to mark the people who benefit from the action.

So both are possible:

• покупать еду для всего класса
• покупать еду всему классу

The version with для is very transparent for learners because it directly matches English for.

Not completely. Russian word order is fairly flexible, although some versions sound more natural than others.

Your sentence is normal:

• Брат шутит, что он ещё не достаточно щедрый, чтобы покупать еду для всего класса.

A slightly more natural variant for many speakers would be:

• Брат шутит, что он ещё недостаточно щедрый, чтобы покупать еду для всего класса.

Russian changes word order mainly for emphasis, rhythm, or style, but the basic relationships are still shown by case endings and verb forms.