"or" usage for choices
"____或____" = "____or____"


Example : 

我沒有姐姐或(者)哥哥 (I don't have sister or brother)


  "是____或是____" = "is ____or____"


Example : 

來的是姐姐或是哥哥都不要緊 (It doesn't matter the one who comes is sister or brother)

~


  "或____或____" = "either____ or____"


Example:

全部隊員或(者)死或(者)傷，我们已經沒法再戦 (All team members either died or injured, we can fight no longer) 


  "或是____或是____" = "is either____ or____"


Example:
來的或是姐姐, 或是哥哥, 總之不會是父母 (The one who comes is either sister or brother, in short, will not be parents)


  I was about to write 我沒有或姐姐或哥哥。


As user6065 stated:

我既沒有姐姐也没有哥哥 (I have neither sister nor brother)

我既有姐姐也有哥哥 (I have sister and also brother)