hi my pups are 6 weeks old and poor mum is looking really thin so she is now not really feeding them , but her teats are bulging and so tight ,should i just leave them ?

If the bitch is looking really thin, is this because she wasn't on 6-7 meals a day?  The body has to draw on all its reserves, and your bitch has been working really, really hard.

Make sure that mum is getting lots of a quality puppy food, and plenty of protein too.  Has she gotten thin because she wouldn't eat?  If she is only on a dry feed, that could be your answer.  Sore mouths from cleaning puppies is so difficult for them.  Ensure that she is given plenty of wet feed.  A bowl of Nutrilac may be welcome.

Pups will be eating well on their own now but she may well want to spend time with them, playing and teaching them their manners.  I let bitches choose when they want to be with pups.  Her milk will be tailing off soon, let it happen naturally unless you suspect a problem - in which case a vet visit would be sensible.

Keep your girl on high nutrition and puppy food for a couple of months.  Her coat will appreciate it too at this stage.

If the pups are 6 weeks old they really don't need mum any more, she's need a break, get her back on a good quality food, the pups will survive without her feeding them.   Obviously don't keep her away from them, but she certainly doesn't need to feed them now.

Feed her more, and let her in to her pups only a couple of times a day. Her milk will slowly dry up.

Although it may look as if they aren't getting much from her, at this age they will be taking the milk faster so need less time suckling, they are still getting nourishment from her ;)

As Jean, I have always fed the bitch on soaked kibble and 'wet' puppy foods 5-6 times a day, meaning the bitch gets all she needs ;)

Left to nature the bitch will dry up naturally. 

At this age the pups need the dam to teach them manners and they learn such a lot from her.  As long as she has an escape route that gives her peace when SHE wants it the milk will soon dry up.  Unless she hates the site of them I'd allow her free access at all times.