[cypher]

If you've noticed him getting smaller then it sounds as though he has lost weight which is usually a sign that something is wrong & needs to be checked out, the fur patches on his sides could just be his scent gland but the lump is more worrying, it could just be an infection not necessarily something as serious as a tumour so if you can try to persuade your parents to at least get a diagnosis from the vet & take it from there.
I don't think you can add photos until you've done a few posts, can't remember now it's been such a long time! But you do it by using the go advanced button below the reply box then scroll down to manage attachments or you can upload photos to a host site like Photobucket & post the link directly.