No puedes culpar a tu hermano.

In Spanish, no normally goes directly before the conjugated verb. Here, the conjugated verb is puedes, so you get No puedes.

• No puedes culpar a tu hermano = You can't / mustn't blame your brother
• Puedes no culpar a tu hermano is also possible, but it means something different: You can choose not to blame your brother

So the position of no matters.

Puedes is the tú form of the verb poder in the present tense.

• yo puedo
• tú puedes
• él/ella/usted puede

Spanish often leaves out the subject pronoun, so No puedes... already means You can't... without needing tú.

Also, poder is a stem-changing verb:

• poder → puedo, puedes, puede...

The o changes to ue in stressed forms.

Because after poder, Spanish uses another verb in the infinitive.

So:

• puedes culpar
• puede hablar
• podemos salir

This is the same basic pattern as in English with can + verb.

That a is the personal a. Spanish usually uses it before a specific person who is the direct object of the verb.

So:

• No puedes culpar a tu hermano
• Veo a María
• Conozco a tu padre

But with things, you usually do not use this a:

• Veo la casa

The a does not mean to here. It is just a grammar marker for a person as the object.

Because tu and tú are different words:

• tu = your
• tú = you

Here you need the possessive adjective tu because it goes with the noun hermano:

• tu hermano = your brother

If you wrote tú hermano, that would be incorrect.

Yes. Tu is informal singular, used when speaking to someone as tú.

A formal version would be:

• No puede culpar a su hermano

You could also include the subject for clarity:

• Usted no puede culpar a su hermano

If speaking to more than one person in Spain, an informal plural version would be:

• No podéis culpar a vuestro hermano

Yes. In standard Spanish, the direct object pronoun would usually be lo:

• No puedes culparlo
• No lo puedes culpar

Both are possible:

• attached to the infinitive: culparlo
• placed before the conjugated verb: lo puedes culpar

In parts of Spain, you may also hear le with a male person:

• No le puedes culpar

That is a common feature called leísmo. For learners, lo is the safest standard choice.

Yes, but the normal, neutral order is:

• No puedes culpar a tu hermano

Spanish can move things around for emphasis, but that usually sounds marked or literary. For example:

• A tu hermano no lo puedes culpar

This gives extra emphasis to a tu hermano. As a learner, the original order is the best one to use first.

Because Spanish normally does not use an article before a noun when a possessive adjective like tu comes before it.

So you say:

• tu hermano
• mi casa
• su coche

Not:

• el tu hermano

The possessive already does the job that the article would normally do.

You can use the pattern:

• culpar a alguien de algo

So for example:

• No puedes culpar a tu hermano de todo
• No puedes culpar a tu hermano de lo que pasó

In your original sentence, only the person is mentioned, so de + thing/reason is simply left out.

In Spain, puedes is pronounced roughly PWEH-des.

A few useful points:

• ue forms one sound together, like a diphthong
• the d between vowels is usually softer than the English d
• stress falls on the first syllable: PUE-des

So the sentence sounds roughly like:

• No PWEH-des cool-PAR a too er-MA-no

That is only an approximation, but it can help at first.