Greyssi and Greyci are (wrong) attemps to spell in Spanish the English
Gracie (the Spanish form of
Grace is
Gracia and its nickname is Gracita and a possible petform would be Graci). They are wrong spellings in Spanish because in this language there are not double SS and the Y is only a consonant or a semiconsonant but only at the end of the word (rey), never in the middle of a word before a consonant (reina).
This kind of Spanization of English names is popular in some Latin American countries and basically among people of low class. If you are interested in the connotations and consequences of this phenomenon and you read Spanish, there are several very interesting
Daniel Samper Pizano's articles and a recent study from the Universidad de los Andes.
Lumia
http://onomastica.mailcatala.com