Mi padre a la piscina con nosotros
-tienen
-es
-va
-da
-son

Va is the conjugation of the irregular verb ir for the third person singular in the simple present. The simple present tense is used to talk about habitual actions or routines. This tense is also used to describe things that happen now or in the near future. To contrast this, es comes from the verb ser (to be), da comes from the verb dar (to give) and son also comes from the verb ser. Finally:

Mi padre va a la piscina con nosotros

answer: the answer is b. se quejan because it's in the plural form.