I'd be very wary of newly treated sleepers, depends what they are treated with, it could be toxic?

Sorry Pam,. but newly treated sleepers will not be treated with anything toxic. The old stuff (Creosote) is no longer allowed to be used. Worth checking though, just in case.
Why do you need to put down weed suppressing membrane? As long as the area is weed free then it is not needed.
Do I presume the chippings are going inside the sleepers and to the depth of the sleeper, say 5 inches?
The sleepers should be heavy enough to stop in place without being anchored.

Thats good to know Ob, I was just being cautious.......

2ft timbers won't be heavy enough to be sure that they won't move. If you can lift them then they can move. If you buy from a reputable supplier there should be some indication of the life of the timber - hardwood will last longer than softwood; pressure treated will last longer than dipped.

Sorry misread that as 10 feet long by 5 inches high. No they would not be heavy enough to stay in place. they would need fastening down somehow.

I have bought new sleepers from two different sources..same size. The first ones weighed about four times as much as the second lot. So it's difficult to say. I would always use a weed membrane for a path. Saves so much work later. If the sleepers are a decent weight they should stay in place if you dig them in a bit. If it's a path I think I would try to keep the membrane in one piece and run it under the sleepers, but it will make it a bit of a fiddle to get the earth up around the sleepers. See how you go. I'm sure it will be great in the end!

I'm going to builders merchant on Friday to see what they are like will report back then ,will probably need more advise from you clever people on this site !!

Check out prices on the Internet as well, and don't forget the delivery charges. If you have to bed them in you might save some money buying slighter smaller - say 8"x 4".