Questions & Answers about Enginn þeirra kemur í kvöld.
Enginn changes for gender, number, and case.
Here it is:
- nominative because it is the subject
- singular because Icelandic treats none in this construction as grammatically singular
- masculine for a masculine or mixed/unspecified group
Other forms are used in other situations:
- engin for feminine
- ekkert for neuter
- engir if you are directly modifying a plural masculine noun, as in Engir gestir koma = No guests are coming
So enginn þeirra is none of them, not no people with an expressed plural noun.