Use TextSource to share single text between several editors. In this case only single copy of text will be stored in memory and editing text in one editor will cause updating all other editors, so they will be synchronized. 

You can also share syntactical analyzer between several editors. To do this you have to assign property TSyntTextSource.SyntaxAnalyzer and reset property TCustomSyntaxMemo.SyntaxAnalyzer to nil. Using single syntactical analyzer will save more time and memory, because there will be single SyntObj.

TCustomSyntaxMemo Properties