Tax credit step children help?

Xnails

I'm going to try keep this short as possible,

I'm thinking about moving in with my girlfriend she is a full time mum on benefits she has 3 children from a passed relationship all under 10 and we have just found out she is expecting again with mine.

On to me I work full time on £300 a week after taxs I have 4 children under 6 from pass relationships which I pay £70 a week child support for.

Now to the question, if we move in together what are we entitled too cause I'm unsure if I can claim working tax credits for her 3 children

Her rent alone is £600 council tax £160

Just scared about not being able to afford it
Any info much appreciated thanks

Xnails

That's good news I'll get on that right away thanks for the quick reply.