So far I've been searching for russian terms of endearment and nick names (as well as scanning the posts here) but I've only been able to find articles on how you create a nickname from a persons given name. I'd rather avoid that if I can - the best would be if I could find something that literally means "brother" or similar. I did find a straight translation for brother (and words like it, i.e. blood brother) but they were in cyrillic and since I don't speak or read russian I didn't feel too confident in using any of them.
General non-name based terms of endearment would also be very welcome. She speaks english fluently but I'd like the option of adding a word in russian here or there if I can to add some flavor.