Dont be too cast down - they can gain ground quickly. Moray was very underweight when we got him (had been left in an empty flat with his sister, with no food or water for 5 days). His coat was dull and there was no inkling of the cat he was to become. Within a month he'd begun to fill out nicely.
Worms will affect a kitten's weight, and given the flea problem, that will have had an impact no doubt. I'd wager a pound to a penny that you and your Mum will have these two turned round in no time. Keep weighing, keep photographing, and you will see them blossom, I promise!
