[AngelicaDeAlquezar]

The translation of "either" depends of the position of the word in the sentence and how it works (there are many ways to translate it). In your examples, it could be "o" (or nothing at all):

- Vas con ellos o te quedas conmigo o te quedas aquí.
- La respuesta es sí o no.


When you say "I don't want to stay here, but I don't want to go with them either", you use "tampoco":

- No me quiero quedar, pero tampoco quiero ir con ellos.