Who are they and what do they represent?

They were the people that lived next to the dude with orchids who hung himself.

Go gentle, I'm English, it's my 1st post and it is the 4th of July.

Peter 

Imperialist!
j/k  Welcome

The boy in the mask is from FWWM, he's called The Jumping Man.

The Grandson is the boy magician who lives with Mrs. Tremond, next to Harold Smith.

Also known as the Chalfonts, they are inhabiting spirits like BOB and Mike. They seem to want to help Laura and Donna.

We still are imperialists. It's just that we don't have an empire!!!

Thanks for the info - really helps understand - another piece in place. 

The Jumping Man (per the credits) is the lodge inhabitant who also wears a mask and jumps around, but his mask has a mouth to it, and the character is a black man in a red suit.

 The Jumping Man is played by Carlton Lee Russell. He seems to be a black guy as he's performed on The Living Color in a sketch called "Black People Awards" and he plays the frozen Gary Coleman on Austin Powers.

 At first I thought that The Electrician was the guy working with the lamp at Hap's Diner but as the actor of The Electrician is black then it can't be him. :D So, yeah, I think Calvin Lockhart has only that minor role as the guy who says "electicity". It always could be so that he had more to do and say but it didn't end up in the final cut. Just as what happened with Jürgen Prochnow (he just sits there with his fake beard and does that "one-hand-clap" with his arm, although he had more to do according to the script).

yeah, that scene at hap's was the only thing i could think of as possibly involving the Electrician, but that guy looks more like Toad from the series than Lockhart. ;) what a shame, now that i think of it, that not only are we missing scenes of most of the rest of characters from the series, but also of the more metaphysical and/or psychological aspects and characters, such as the woodsman(Prochnow) you mention. doubtless the rest of the lodge spirits as well. what a tease.
and to the subject at hand, i dont think the tremond/chalfont boy and grandmother(who i had always sort of associated with lynch's short film, the grandmother) are inhabiting spirits. spirits yes, but they are always in the same physical form, unlike bob, and mike previously, they dont take over mere mortals(and taking into acount their altering of reality in the series too) they seem to act empherially. as to what they actually represent, i think thats hard to put into words. but thats how they work for me as characters.

Along the back wall, left to right:  Jumping Man (Carlton Lee Russel), Electritian (Calvin Lockhart), Mrs Tremond/Chalfont (Frances Bay), Grandson (Jonathan J. Leppell [played by Austin Jack Lynch in the series]), Second Woodsman (David Brisbin ["Mr. Ernst" of HEY DUDE fame]), and Woodsman (Jürgen Prochnow).  The others I believe you already know.

I always thought that the Jumping Man was connected to or was a representation of Bowie's character. The way the shot fades into him after after Bowie says "We lived above a convenience store" and "I've been to one of their meetings" suggested to me that they are the same person or connected in some way. Did anyone else get this from seeing it?

actually when the FBI office scene segues to the convience store/lodge through static, bowie says, pointing at cooper "just who do you think this is there?"(notice how he is looking at coop while talking about judy right before). so a theory i have come across is that the jumping man is connected to cooper, as the line is said exactly when the jumping man fades onto the scene then disappears. im not totally convinced, i know time doesnt exist in the same way in the lodge if at all(although this is the convience store, so maybe it does), either way, im not convinced of this explation personnally. as it is not clear if the scene in question is a depiction of what jefferies saw, or just an abstraction of all the lodge elements. also some have theorized that the grandson is bowie(the monkey/judy connection). again, something i think is up for interpetation, not conclusion.
speaking of conclusion, after rewatching the scene due to geoffr111 posting that frame with the brightness totally beyond what is on the american release, i cant help but notice lockhart now. i guess i was distracted by either the foreground(LMFAP&BOB) of the middle ground(the jumping man), therefore lulled into not looking close enough at the background(who i already knew included the tremonts/chalfonts and the two woodsman)(tho, in my defense, until recently i have relied on the original VHS version, very well worn, as i was refusing to by the DVD until they added the exercised scenes, but i recently broke down and gave up and bought the DVD. HUGE diverence) anyway hes plain as day now as i cant believe i never noticed him in the two short shots that include the whole room. now what the hell is he doing there i guess is the quetion.

"Harry, I'm going to let you in on a little secret. Every day, once a day, give yourself a present. Don't plan it, don't wait for it, just let it happen. Could be a new shirt at the men's store, a catnap in your office chair, or two cups of good, hot, black coffee. Like this."  -Dale Cooper

Quoting Wikipedia:
"Some time before the events of the series, it is revealed that the Log Lady's husband was a lumberjack who died in a fire on their wedding night decades before. (The Log Lady later says that her husband "met the devil"), Nothing is revealed of her husband beyond this, save for that at some point before he died, her husband returned from a trip to Glastonbury Grove (which served as an access point to the metaphysical realms of both the White and Black Lodges) with a jar of mysterious oil, which he claimed was for "opening a gateway."

My interpretation of the scene in the above picture, was that it somehow represented the "birth" of the Black Lodge, or at least some other formal/ritual occasion as implied by the "wedding" which takes place between Mike's Arm and Bob. Shortly thereafter, they are both seen entering the Black Lodge through the curtain.

Quoting tvacres.com

Her log (a piece of Ponderosa Pine) was a gift from her firefighter husband on their wedding day. Unfortunately, he died the next day while fighting a forest fire.

"Harry, I'm going to let you in on a little secret. Every day, once a day, give yourself a present. Don't plan it, don't wait for it, just let it happen. Could be a new shirt at the men's store, a catnap in your office chair, or two cups of good, hot, black coffee. Like this."  -Dale Cooper

EDIT:  Hmmm... I THOUGHT the tvacres info was quoting from the StarCards, but they actually say her husband was a woodsman.  Not that we should trust them anyway.  I don't know where that information comes from.

As a side note, I see in my searching that PIERRE is listed as the grandson's name in the StarCards.  But again, these aren't cannon.  He's never called that in the show or the movie as far as I remeber.