The present progressive is used when talking about something that is happening now. The present progressive is usually formed using the verb estar plus a present participle following the formula:
estar + present participle
1. está trabajando
Here we use two words está and trabajando. The first word comes from the verb estar and is the conjugation of this verb for the third person singular in the simple present. This sentence stands for the third person singular because Mi padre can be replaced by the subject pronoun that matches this person, which is él (he). On the other hand, trabajando is the present participle of the verb trabajar.
2. están trabajando
Here we use two words están and trabajando. As in the previous sentence, the word trabajando is the present participle that comes from the verb trabajar. On the other hand, están is the conjugation of the verb estar for the third person plural in the simple present. This sentence stands for the third person plural because Mis primos can be replaced by the subject pronoun that matches this person, which is ellos (they).
3. estás tomando
Here we use two words estás and tomando. The first word comes from the verb estar and is the conjugation of this verb for the second person singular (tú - you in English) in the simple present. On the other hand, tomando is the present participle of the verb tomar.
4. están corriendo
Since there are some people who are running in the park, this sentence stands for the third person plural. Hence the conjugation of the verb estar we need to use must match this person as well, which is están. On the other hand, corriendo is the present participle of the verb correr.