"algunas" is formed with "algun+a+s"
where the "a" is the feminine and the "s" is plural.
Algun means "some": algun pais: some country, algun amigo: some friend
so algunas means some for femininine plural: some parties.
party, Fiesta is feminine in spanish, so you need a feminine version of algun.
and the sentence means: some parties are celebrated in the house (casa not case!) of the family
well, in this context, fiesta can also be a "celebration" or "holiday", not only a party
so it means "some unspecified ones"
What is that supposed to mean
1) Aquellas, éstas
2) Esos, aquellos
3) Aquellos, estos
4) Esta, aquella
5) Este, ese
6) Esas, aquellas
7) Estos, aquellos
