[SueM]

Is there anything i can do to help the fry survive (with the net maybe)?
Yes, toss it in, anchor some to the bottom, but let it travel & float to the top, when live bearers are first born, they need to go to the top asap to fill their air bladders, so give them a way out.

Also would a 4cm bristle nose catfish eat the fry?
No
And is it true when the mother gives birth she goes through a phase were she isn't hungry?
Yes, and she also finds a more hidden spot to have her babies, this gives them a little more of a chance. But the "not hungry" stage only lasts as long as her child birth, so the more outs you give the fry the better.

BTW, thank you for not wanting to use breeder traps, more females die during birth do to the added stress.