First of all - please don;t panic. There is an awful lot of stuff on-line that is totally incorrect. Bumblefoot is manageable if not curable (depending upon the cause)......
without the need for amputation - .
Second - without a picture, we do not know whether or not your piggies actually have bumblefoot - which is a bacterial infection of the paws and can be accompanied by scabs/open wounds. You describe the feet as "looking like tumours" but some piggies do have very fleshy paws....and what do you mean anyway by "looking like tumours?" Please upload photos as soon as you can.
Thirdly - IF it is bumblefoot - it would point towards a heart problem or diabetes - infections in the extremities normally only appear if the circulation is compromised by an underlying condition.
Fourthly the only other ways infection sets up in the paws is by
a) repeated and constant exposure to harsh conditions/chemicals such as urine
b) by trauma - open wound
The most important thing is to determine whether they have bumblefoot or something else....then what may have caused it (e.g. urine or heart condition) - you can instigate treatment in the form of antibiotics but without determining the cause this condition will just repeat.
In the meantime espom salts or diluted hibiscrub bathing may help.....or application of a barrier cream (nappy rash) such as sudocream may help protect providing there are no open wounds/breaks to the skin. Most importantly however they need to be checked by a vet pronto and, if necessary, anitbiotics prescribed.
Hibiscrub can be bought from an on-line chemist - I notice you are in Ontario canada - so google your on-line suppliers. Failing that Amazon.com (prob more expensive) have a supplier who would appear to ship overseas.
http://www.amazon.com/Scrub-Chlorhexidine-Antimicrobial-Cleanser-500ml/dp/B00A4BSQ2Y
HTH
x