just a thought, why not bring your rabbit indoors and have him live with you? My friend has a house rabbit, and she was lovely.
Also, I don't think guinea pigs are good companions for rabbits, but i can't remember why!
We had 2 sisters, that turned out to be a brother and a sister and ended up with 9 babies! We kept one baby so now have three.
They have all been neutured to avoid fighting. The original two are sometimes a bit mean to the baby and you rarely see them all snuggled together.
We do have a chicken tho, and she gets on with them all.
As i say, it's quite tricky, and i read loads of stuff when we found the babies. There are some very good sites. I do think you are doing the right thing for your lonely rabbit though . let us know how you get on.