My name isXXXXX I can try to help answer your questions about your guinea pigs
The answer is it depends on the individuals. I have 2 male guinea pigs and was also worried about aggression when I introduced them. They did squabble a few times over the 1st couple weeks, but nothing serious enough to create wounds on each other. The pecking order was eventually established and now they are best buds.
Of course it makes sense to get the same sex because there wont be issues with breeding and/or you don't have to worry about the spay/neuter aspect of things.
I would suggest keeping a close eye on them during introduction. I little bit of rough play is okay but separate them if the squabble seems serious.
If the current enclosure belongs to one guinea pig currently, it may help if the initial introduction is on neutral territory, like a floor. And it also helps to clean the cage thoroughly to help eliminate strong urine odor right when the new one is introduced.
Provide 2 food bowls and 2 water stations on separate ends of the cage.
Hopefully this helps, feel free to respond with further questions.
I dont know if You realize it or not but I was also the person who got Your advice for My African Grey Ganny...as far as the guinea pigs..My granddaughter hasnt decided yet if She is getting Him a buddy....
I have been giving Ganny the benedryl bid like You said...I also bought Him rice cakes...unsalted...(Can they have salted...would salted be harmful?) & I also was going to ask You about giving Him & My little cockatiel millet spray...is that ok to give them? They love it...& I think thats something healthy....or no??
I wrote You yesterday....You havent responded back yet...???.>>.