You wouldn't add anything to pluralise the surname Muniz, you could just say "The Muniz are coming over"
If Gelpi is a surname, then the plural is Gelpis.
The plural of the surname may be Simmons or Simmonses.
The surname Hester has the plural Hesters (two Hesters, or the Hester family).
The plural form of Hass is Hasses, e.g. All the Hasses were invited to the wedding.
Winters. Plural of winter is winters. Plural of surname Winters would also Winters. Possessive of winter would be winter's.
The plural form of the surname Gillis is Gillises.
The plural of Shastri would be Shastris
If Gelpi is a surname, then the plural is Gelpis.
If Hoix is a surname, then the plural is Hoixes
The plural of the surname may be Simmons or Simmonses.
The plural of the surname Sarli would be Sarlis.
The plural of bràthair (brother) is bràithrean. (This would not be for the surname Brothers.)
A surname cannot be pluralized.
The plural form of the proper noun Justiz is Justizes.
In English, the plural is Mullinaxes Other languages make plurals differently.
The surname Hester has the plural Hesters (two Hesters, or the Hester family).
The plural form of Hass is Hasses, e.g. All the Hasses were invited to the wedding.