Anstataŭ ke mi malstreĉas la ĉenon, mia frato kontrolas la radon.

Anstataŭ ke introduces a clause meaning instead of the fact that... / rather than....

So the sentence sets up a contrast or replacement between two actions:

• mi malstreĉas la ĉenon
• mia frato kontrolas la radon

A simple way to think of it is: one action is being presented instead of the other.

English often says something like instead of loosening the chain. Esperanto usually does not use an English-style gerund in -ing that way.

If you want a full clause with its own subject and verb, Esperanto uses ke:

• anstataŭ ke mi malstreĉas la ĉenon

That is why you see ke here.

If the subject is the same in both parts, Esperanto often prefers a simpler infinitive construction, for example:

• Anstataŭ malstreĉi la ĉenon, mi kontrolas la radon.

Not in this exact structure.

Here you have a full clause after anstataŭ:

• mi malstreĉas la ĉenon

With a full clause like that, ke is the normal linker.

You may see anstataŭ ol with an infinitive, but that is a different pattern. So:

• anstataŭ ke mi malstreĉas... = full clause
• anstataŭ malstreĉi... = infinitive construction

For this sentence as written, ke is the appropriate choice.

Usually, yes. Anstataŭ normally suggests replacement: the second action happens in place of the first one.

So this sentence tends to suggest:

• your brother checks the wheel
• rather than you loosening the chain

If you wanted to say both actions happen at the same time, Esperanto would more naturally use something like dum (while) or simply another structure.

Malstreĉas is possible here.

After ke, Esperanto can use a normal finite verb, and -as gives a present-time statement. So anstataŭ ke mi malstreĉas... is understandable and acceptable.

You may also encounter -u in similar sentences:

• Anstataŭ ke mi malstreĉu la ĉenon...

That can give a more intended, expected, or non-realized feeling. In other words, -u can make the first action sound more like something that would be done or was supposed to be done.

So:

• malstreĉas = a straightforward present-clause wording
• malstreĉu = can sound more hypothetical or intended

It has three parts:

• streĉ- = tighten, stretch, strain
• mal- = the opposite
• -as = present tense

So malstreĉas means loosens, slackens, or is loosening.

This is a very typical Esperanto word-building pattern: take a root and add mal- to reverse the meaning.

Because they are direct objects.

In Esperanto, the direct object takes the accusative ending -n.

Here:

• mi malstreĉas la ĉenon → what do I loosen? la ĉenon
• mia frato kontrolas la radon → what does my brother check? la radon

That is why both nouns have -n.

Esperanto -as is the general present tense. It can correspond to several English present forms, depending on context:

• checks
• is checking
• sometimes even does check

So:

• malstreĉas can mean loosens or is loosening
• kontrolas can mean checks or is checking

Esperanto usually does not force the same simple/progressive distinction that English often does.

La means the. It marks something as specific or known in context.

Here, the sentence probably refers to a particular chain and a particular wheel, not just any chain or wheel. For example, if people are working on a bicycle or machine, those parts are specific and identifiable, so la is natural.

Yes: in Esperanto, kontroli usually means to check, inspect, verify, examine.

This is a common false friend for English speakers. It usually does not mean English to control in the sense of govern, direct, or operate.

So here:

• mia frato kontrolas la radon = my brother checks the wheel

not

• my brother controls the wheel

Yes.

The sentence begins with a subordinate clause:

• Anstataŭ ke mi malstreĉas la ĉenon

and then gives the main clause:

• mia frato kontrolas la radon

Putting a comma between them is normal and helpful.

Esperanto word order is fairly flexible, because endings show grammatical roles, but this order is straightforward and natural.