Answer and explanation:
By using the stated sentence structure above, ir a + an infinitive form of a verb (meaning, not conjugated), the correct answer would be the following:
Martín y Rodolfo van a ir a nadar en la piscina mañana también.
This sentence translates into: Martin and Rodolfo will also be swimming in the pool tomorrow.
As a native Spanish speaker, this is the correct form of the sentence.
