It's also possible, as others have been suggesting, that Lesath's father is not Rodolphus but Voldemort.

Latest chapter (http://www.fanfiction.net/s/5782108/63/) seems to put the kibosh on that:

"I understand, my Lord," said the older boy, his voice wavering a little, "you do not trust my cunning, and indeed I have shown myself a fool... I only wanted to say to you, that I am not ungrateful, that I know it must have been hard enough to save only one person, that they're alerted now, that you can't - get Father - but I am not ungrateful, I will never be ungrateful to you again. If ever you have a use for this unworthy servant, call me wherever I am, and I will answer, my Lord -"

Obviously makes no sense if 'Father' is Voldemort; Lesath could be mistaken or deceived, but of course that's a more specific scenario and so less likely.