With the CSA it depends on what he is earning, they take out a percentage, but not sure what it will be, it all depends on how much he earns, they also take into consideration his living expenses....and im not being funny, but I would rather have �44 rather than nothing! Although in saying that, with what he earns, I cant see it being that, not in a million years.
Your sister is taking on all the responsibilty herself why he walks around like a single man with no ties...not fair, she needs to act on this! good luck x