advice on calculation with new familly

Im hoping someone can advise.
I currently live with a partner, I also have 2 children by a previous
marrige.
I have 1 child with the new partner
I have 2 step children
I get a waged income of 100 quid.
I have paid to me a benefit via the inland revenue working famillys
tax credit of 125 quid a week.
1 of my step children is disabled.

The rest of the family tax credits, child tax credits we get are in my
new partners name.

Can any of you tell me how each of these things is viewed by the CSA,
and what my moves should be.
It is begining to look like my new partner might have to ask me to
leave my familly home as the stupid new familly tax credit system pays
125 quid of it to me!!! and therefore i think it might be thought of
as part of my net income.
(they are not part of my net income in my opinion as they are paid to
me for my step kids and child due to me not earning enough)