It's a commitment.
We had two but are down to one. With two, I had to clean the cage twice a week to contain the smell. Also, the cage needs to be located in an area where your family is routinely.
The cages they sell at the pet store are not big enough. This is the smallest one I would recommend:
http://www.amazon.com/Midwest-Homes-for-Pets-171GH/dp/B001NJ0DPY/ref=sr_1_2?s=pet-supplies&ie=UTF8&qid=1420557306&sr=1-2&keywords=guinea+pig+cage
Does anyone in your family have seasonal allergies? If so, before getting the guinea pigs, buy a big bag of the Timothy hay that they will absolutely need. Bring it home and place a large quantity in the open in the area where the cage will be and see if anyone has a reaction or it brings on allergy symptoms.