Estamos a punto de arriesgarnos.

Because estar is used for a temporary state or situation, and a punto de + infinitive is a fixed expression meaning to be about to do something.

So:

• estamos a punto de... = we are about to...

Using ser here would be wrong.

A punto de means on the point of, just about to, or more naturally in English, about to.

It is followed by an infinitive:

• Estoy a punto de salir. = I’m about to leave.
• Estamos a punto de arriesgarnos. = We’re about to risk it / put ourselves at risk.

The de is required in this structure.

Because the expression is estar a punto de + infinitive.

So the pattern is:

• estar
• a punto de
• infinitive

Examples:

• Está a punto de llover.
• Estamos a punto de empezar.
• Estamos a punto de arriesgarnos.

You cannot normally leave out the de here.

Yes. Arriesgarnos is the infinitive arriesgarse with nos attached.

Breakdown:

• arriesgar = to risk
• arriesgarse = to take a risk / to put oneself at risk
• arriesgar-nos = to risk ourselves / to put ourselves at risk

In this sentence, nos refers to we/us, so arriesgarnos means something like:

• to risk ourselves
• to put ourselves in danger
• sometimes more naturally, to take a risk

Depending on context, it may be literal or figurative.

Because arriesgarnos is an infinitive, and object/reflexive pronouns can attach to the end of an infinitive.

So:

• arriesgarnos = arriesgar + nos

This is normal after expressions like estar a punto de.

A form like Estamos a punto de nos arriesgar is not standard.

With a conjugated reflexive verb, the pronoun goes before:

• Nos arriesgamos. = We take a risk / we risk ourselves.

But with an infinitive, it attaches:

• ...de arriesgarnos

No, that is not correct.

The structure here is not estar + gerund. It is:

• estar + a punto de + infinitive

So the correct sentence is:

• Estamos a punto de arriesgarnos.

If you want a sentence with the pronoun before a conjugated reflexive verb, you need a different structure, for example:

• Nos vamos a arriesgar. = We’re going to take a risk.
• Nos arriesgamos. = We take a risk / we’re taking a risk.

It is implied by estamos.

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

So:

• Estamos a punto de arriesgarnos.

already means:

• We are about to risk ourselves / We’re about to take a risk.

You could add nosotros/nosotras for emphasis:

• Nosotros estamos a punto de arriesgarnos.

But normally it is unnecessary.

Not exactly.

• arriesgar usually takes a direct object: to risk something

  • arriesgar dinero = to risk money
  • arriesgar la vida = to risk one’s life

• arriesgarse means to take a risk or to put oneself at risk

  • arriesgarse a perderlo todo = to risk losing everything
  • arriesgarnos = to risk ourselves / to put ourselves at risk

So in your sentence, the reflexive form is important.

By itself, arriesgarnos focuses on us as the ones exposed to danger or risk.

If you want to specify what is being risked, Spanish often uses arriesgar plus an object:

• Estamos a punto de arriesgar todo. = We’re about to risk everything.
• Estamos a punto de arriesgar nuestra reputación. = We’re about to risk our reputation.

If you want both ideas, Spanish can combine them differently depending on context, for example:

• Estamos a punto de arriesgarnos mucho.
• Estamos a punto de arriesgarlo todo.

Yes, it is natural and grammatical in Spanish from Spain.

That said, depending on context, a native speaker might also say:

• Estamos a punto de correr un riesgo.
• Estamos a punto de jugárnosla. (more colloquial)
• Nos vamos a arriesgar.

But Estamos a punto de arriesgarnos is perfectly understandable and natural, especially if the idea is we are just about to put ourselves at risk.

A simple Spain Spanish pronunciation guide would be:

ehs-TAH-mos a POON-to de ah-rree-ES-gar-nos

A few points:

• estamos has stress on ta
• punto has stress on pun
• arriesgarnos has stress on gar
• the rr in arriesgarnos is a rolled/trilled r
• in Spain, z is pronounced like the th in think, but this sentence does not contain z

So arriesgarnos is the part many learners will want to practise most.