Yes they can if your garden is big enough
Ginnea pigs can be kept in a hutch outside in the garden, or in a large cage inside. Out in the garden will reduce the smell however having them indoor is more convenient for handling and feeding.
I think pigs are probably kept in a pen.
Pigs are only of use to break up rough ground as they grub about. They would cause devastation in an open garden.
Guinea pigs can be kept at room temperature, I have two of them.
As a pet pigs aren't exactly the best animal to have as they need mud etc. But if you have a garden then dwarf pigs are the best but if you have a big garden or a farm then just normal pigs are fine.
No they should be kept in a hutch or a cage.
A back garden is a garden towards the rear of a property.
Yes, on most farms the pigs are kept clean and sanitary.
Yes they can
A bear garden is a public place where bears are kept for diversion or fighting.
I wouldn't recommend it.
Messy area/area where pigs are kept