My mum's two pups have had problems with pooing for the last week or so.  They cannot pass it even though it is soft when it eventually comes out.  They have been in so much pain with it especially the biggest boy. 

Due to the straining and pain for the last week and a half his back legs are now really weird when he walks and really splayed out.  Do you think tht they will ever go back to normal or is it possible that all the straining etc. has caused problems with his hips/bones?

What has the vet said?

Nothing much, just told my mum to keep doing what she's been doing and charged her £20 for the advice :d

I would have thought the vet would want to investigate why they're having trouble pooing in the first place?

Yes, I agree with Annie, the vet should be investigating.  go back to the vet and if you are not satisfied ask for a second opinion, about both problems!
 

Well they are much better now.  The backend on the biggest is still not correct but the left leg is fine now and the right one is getting back to normal slowly.

They are sooooo cute :d  I want one but I don't think that my mum will let me :d