How can i tell if my guinea pig pregnant?

Question
I have a to female guinea-pigs and a male. They do not sleep in the same cage but share a run (that there in ALL day).
One Guinea pig is 5 years old and apparently can't give birth.
And my other gunea pig is about the same age as the male.
Would the male mate with both guinea pigs?
Also how can i tell if she IS pregnant?

Answer
I wouldn't let them play together unless you neuter the male. Please do not put them together anymore. If your sows happen to not be pregnant, they will be if you keep putting them together. If your sows give birth while in the run with the male, he will impregnate them again.

Of course the male will mate with them.

A 5 year old sow can get pregnant, but she will likely have complications at that age and it will be very hard on her body. It's risky for any sow to be pregnant, but it increases with age.

You can't tell for sure unless your vet does an x-ray or ultrasound. You should be able to feel movement at 6 weeks. You can weigh daily and see if they gain.

Please read these links:
http://www.guinealynx.info/reproduction.html
http://www.cavyspirit.com/breeding.htm
http://www.guinealynx.info/breeding.html