Who Can Live With Who?
On the whole, the following is true:
Males and females can live together quite happily but you must be prepared for the consequences Does breed continuously throughout the year and it would be very unfair to breed her so many times, not to mention the effect it would have on her general health. I personally have never put a male and female together for longer than a few hours when I wanted them to breed.
Males very rarely live with other males. They tend to get territorial and one will try and dominate the other. This will usually result in serious injury or even death. Some males may tolerate each other when they are outside of their hutches (in a run or the garden) as opposed to being kept together in 1 cage.
Females will nearly always live happily with another female. This is particularly true if both Does have been introduced from a very early age, or are from the same litter. You may, sometimes, be able to introduce an older female to another one but I suggest you watch them closely for a few days to make sure they do not fight. Does make better pets as they have a better temperament than bucks and will quite happily live together without fighting.
Males can be neutered and then they will be able to live with the female and you will not have to worry about an unwanted pregnancy. This is great because they get companionship which makes them happy and healthier. Neutering male/male and female/female pairs also means they are more likely to live together without fighting.
The RSPCA advise against keeping Guinea Pigs with rabbits as they have different dietary needs, have different ways of communicating and rabbits can do very nasty injuries to them.