How do I train these little rascals?

I just adopted two 7 week old kittens 2 days ago. They are brothers. I am trying to train them to use the litter box but have been unsucessful so far. They keep doing their business on my bed!!!! I had another cat but he got real sick and I had to put him down. I remember the last day I had him he urinated on the bed (very unusual behavior for him, but he was sick...he was litter box trained in minutes when i got him as a kitten). This occured about a month ago. I scrubbed my bed several times since then and I do not smell anything. Is it possible that they keep going potty on my bed b/c they smell my old cat? How do I train them?!?!?!