Is it normal for litter mates to fight or bluff fight and bark at each other a lot?

From what I've observed, alot has to do with the breed, and parents.

You get a litter of house companion labs, and they will play fight and bark at each other some. You get a litter of high drive KNPV dutch shepherds or Belgian Malinois, and it's like watching an arena sometimes. They have a very noticable difference in the amount of energy and drive they put into playing. I'm sure one of the professional breeders can tell you with alot more certainty, but that's just what I've observed. Kadi? Betty?

It is absolutely typical. It is all part of a baby finding his place in the world, and is even more dynamic in a pack environment, where rank determines everything, starting with who gets the fattest teat. In the animal world, play fighting teaches the skills that will be vital to an animal's survival in the future. Watch any documentary about wild babies and you will see that this is the predominant subject.
While our dogs are highly domesticated, they still have certain basic instincts, including defensive and hunt drives.

My 2 mastiffs are litter sibs, not by design, we took Kaiser in at 8 months, (long story) and Sugar, who we got at 8 weeks, was the one shoving all the other pups off the teats even at a few days old, she still is a bossy mare, and even though her and Kaiser were apart for the first 6 months, he still gets a curled lip from her at times, they don't fight, thank god, but they play really rough, and off lead over the fields, they shoulder barge and tumble each other every opportunity.

Harry, who we lost last year, was their half sib, (same father) and while a very young pup had a great friendship with Sugar, he and Kaiser came to blows all to regularly toward the end, that was predominantly due to Harry's illness, but there was a major difference between the dynamics with the 3 of them.

I know of litter sibs in softer breeds who got on great all their long lives, but I imagine it has a lot to do with the pecking order in the litter, as has already been stated, and to some extent, the breed, and if you are talking about your mastiffs, they are a bit of an oafish breed anyway (as I am sure you already know!) and mature very late, so rough housing is probably to be expected, stopping it getting out of hand with powerful breeds, with a lot if weight behind them is the key of course

It's a normal learning process in a litter. It teaches each one's place in the pecking order and it also teaches bite control. "Bite me to hard and I'll bite back or quit playing with you".
Now here's where I get a lot of disagreement with a lot of people.
To much interference with this interaction between dogs living together can create frustration and lead to greater problems down the road.
Having said this you have to really be able to read your dogs to allow this. Understanding why they are "disagreeing". Genetically disposed dog aggression is a whole different ball of wax. Spoiled dogs where owners want to decide who's top dog among the dogs and most importantly a lack of leadership with your dog(s) and this wont work.

Yes it is, by watching it you can learn a lot about the pups and you do want to make sure that one pup is not being beat up a lot.

Don't let one pup get constantly dominated.