Asumimos la responsabilidad.

Not exactly.

In this sentence, asumir means to take on, to accept, or to shoulder something, especially a duty, role, or responsibility.

So Asumimos la responsabilidad means something like:

• We take responsibility
• We accept responsibility
• We assume responsibility (in the formal English sense)

Be careful: English assume often means suppose or guess, but Spanish asumir usually does not mean that.

Spanish often uses the definite article more than English does.

So la responsabilidad is completely natural here, even if English might just say responsibility without the.

• Asumimos la responsabilidad = We take/accept responsibility

Using la does not necessarily mean one very specific responsibility in the way English the always might. In Spanish, this structure is standard.

Because Spanish usually leaves out subject pronouns when the verb already makes the subject clear.

• asumimos already tells you the subject is we
• so Nosotros asumimos la responsabilidad is possible, but not necessary

You would include nosotros only for emphasis, contrast, or clarity, for example:

• Nosotros asumimos la responsabilidad, no ellos.
  We are the ones taking responsibility, not them.

It can be either one, depending on context.

For asumir, asumimos can mean:

• we assume / we take on → present
• we assumed / we took on → preterite (simple past)

So the sentence by itself is ambiguous:

• Asumimos la responsabilidad.
  could mean We accept responsibility or We accepted responsibility.

Usually the wider context makes it clear.

Because asumir is a direct transitive verb here: it takes a direct object without a preposition.

So:

• asumir algo = to take on / accept something

That is why you say:

• Asumimos la responsabilidad

and not:

• Asumimos de la responsabilidad ❌
• Asumimos a la responsabilidad ❌

Usually, asumimos la responsabilidad is the more natural and standard choice.

Spanish often uses asumir la responsabilidad or aceptar la responsabilidad to mean to take/accept responsibility.

Tomar la responsabilidad might be understood in some contexts, but it is less idiomatic here in standard Spanish.

Good natural alternatives are:

• Asumimos la responsabilidad
• Aceptamos la responsabilidad
• Nos hacemos responsables = We make ourselves responsible / We take responsibility

Because the idea is usually treated as one abstract concept: responsibility.

So:

• la responsabilidad = responsibility

You would use the plural responsabilidades only if you are talking about several separate duties or obligations:

• Asumimos las responsabilidades del cargo.
  We took on the responsibilities of the position.

Yes, but the basic version is the most neutral:

• Asumimos la responsabilidad.

You can change the order for emphasis:

• La responsabilidad la asumimos nosotros.
  We are the ones who take responsibility.

That sounds more emphatic or contrastive. For a normal statement, the original order is best.

It is pronounced roughly:

• ah-soo-MEE-mos

The stress is on mi:

• a-su-MI-mos

A more approximate IPA for Spain is:

• [asuˈmimos]

And responsabilidad is stressed on the final dad:

• res-pon-sa-bi-li-DAD

It is very close in meaning, but the structure is different.

• Asumimos la responsabilidad = We accept/take responsibility
• Nos hacemos responsables = We make ourselves responsible / We hold ourselves responsible

Both are natural, but asumimos la responsabilidad sounds a bit more formal and direct, while nos hacemos responsables can sound slightly more personal or explicit.