Tu actitud tranquila hace que la conversación sea más fácil, incluso cuando no estamos de acuerdo.

Because tu here is a possessive adjective meaning your: tu actitud = your attitude.

With an accent, tú is a subject pronoun meaning you.

• tu actitud = your attitude
• tú eres amable = you are kind

So in this sentence, tu is correct because it is showing possession.

Because tranquila describes actitud, and actitud is a feminine singular noun.

Spanish adjectives usually agree with the noun they describe in gender and number:

• actitud tranquila — feminine singular
• comportamiento tranquilo — masculine singular
• actitudes tranquilas — feminine plural

So tranquila matches actitud.

In Spanish, descriptive adjectives often come after the noun. So actitud tranquila is the most neutral and natural order.

Putting the adjective before the noun, as in tranquila actitud, is possible in some contexts, but it sounds more literary, emotional, or marked. For everyday Spanish, actitud tranquila is the normal choice.

Here hacer que means something like makes it so that or causes.

So:

• Tu actitud tranquila hace que...
  = Your calm attitude makes it so that... = Your calm attitude causes...

It is a very common Spanish structure:

• Eso hace que sea difícil = That makes it difficult
• Su ayuda hace que todo sea más fácil = His/Her help makes everything easier

In your sentence, the subject is tu actitud tranquila, and it causes a result in la conversación.

Because hacer que normally triggers the subjunctive when one thing causes another thing to happen.

Here, tu actitud tranquila causes la conversación to be easier, so Spanish uses:

• hace que la conversación sea más fácil

not:

• hace que la conversación es más fácil

Sea is the present subjunctive of ser.

This is a very common pattern:

• hacer que + subjunctive

Examples:

• Eso hace que me sienta mejor = That makes me feel better
• La lluvia hace que el viaje sea más lento = The rain makes the journey slower

Because Spanish often uses the definite article where English may or may not use the.

Here la conversación refers to the conversation or interaction between the people involved. It sounds natural and complete in Spanish.

Saying just conversación here would sound unnatural. Spanish usually wants the article in this kind of structure:

• la conversación
• la situación
• el problema

Because fácil is an adjective, and here it describes la conversación.

The sentence is saying that the conversation is easier, so Spanish uses:

• la conversación sea más fácil

If you used más fácilmente, that would be an adverb, meaning more easily, and it would need a different structure. For example:

• Hablamos más fácilmente = We speak more easily

So:

• más fácil = describes a thing or situation
• más fácilmente = describes how an action is done

Because not all Spanish adjectives change for gender.

Adjectives ending in -o / -a usually change:

• tranquilo / tranquila

But adjectives ending in many other letters often stay the same for masculine and feminine:

• fácil
• difícil
• útil

So:

• un problema fácil
• una conversación fácil

Only the plural changes:

• fáciles

Because Spanish often omits subject pronouns when the verb form already makes the subject clear.

Estamos already tells you the subject is we. So:

• no estamos de acuerdo = we do not agree

You could say nosotros no estamos de acuerdo, but that adds emphasis or contrast, for example if you want to stress we in particular.

Because the fixed expression in Spanish is estar de acuerdo, which means to agree or to be in agreement.

Spanish uses estar, not ser, because it treats agreement here as a state or position, not as identity.

So:

• estoy de acuerdo = I agree
• estamos de acuerdo = we agree

Also, de acuerdo stays the same; it does not change to match number here.

Incluso cuando means even when.

It introduces a situation where something remains true despite a difficulty:

• incluso cuando no estamos de acuerdo = even when we do not agree

It adds the idea that the calm attitude helps not only in easy moments, but also in difficult ones.

Sometimes yes, but the meaning is slightly different.

• incluso cuando no estamos de acuerdo = even when we do not agree
• aunque no estamos de acuerdo = although we do not agree

Both can work, but incluso cuando focuses more on the specific situation or moment in which disagreement happens. It highlights those moments: even in those cases.

Aunque is more like a general concession: although / even though.

So the original wording is very natural and slightly more precise.

Because cuando here is a conjunction meaning when.

Spanish uses cuándo with an accent in questions or indirect questions:

• ¿Cuándo vienes? = When are you coming?
• No sé cuándo viene = I don’t know when he/she is coming

But in your sentence, it simply links two parts of the sentence:

• incluso cuando no estamos de acuerdo

So it takes no accent.

The sentence breaks down like this:

• Tu actitud tranquila — subject
• hace — verb
• que la conversación sea más fácil — result clause with subjunctive
• incluso cuando no estamos de acuerdo — additional clause giving a contrasting situation

So the pattern is roughly:

[cause] + hace que + [result in the subjunctive] + [even when + situation]

That is a very useful structure to recognise and reuse in Spanish.