If one member owns the DLC for the game it will be accessible to the whole party according to Turtle Rock Studios.
Back For Blood is the highly anticipated survival horror set to be released on the 12th of October this year.
In a quiet unveiling on the official Back For Blood website, the announcement was made they “ will not split the player base by releasing paid post-launch content.” They further explained that: “In PVE, If your party leader owns a paid content drop, you will be able to play that content with them — including maps, gameplay, and campaign.”
“No separation. No exclusion. No split.”
On the PvE side of the game, although paid DLC such as new playable characters, items, and more will be available, all of this material may be gained through in-game progression.

In the game’s PvP mode, one team plays as humans, while the other plays as ‘the Ridden.’ Both sides take turns trying to stay alive as humans for as long as possible, while the Ridden players try to kill them by playing as elite infected. The team that is able to stay alive as humans for the longest time wins the game.
The game’s overview is the game takes place after a worldwide outbreak triggered by a newly discovered parasite, (which is heavily implied to be of alien origin). The “Ridden” have infected the majority of humankind, leaving players in a post-apocalyptic world.
In this world, the “Cleaners,” a group of veterans, get together to fight the zombies. The cleaners’ names are Walker, Holly, Hoffman, Evangelo, Karlee, Doc, Jim, and Mom.
Cards are a new feature in Back 4 Blood. Players must create their deck with cards that affect several aspects of gameplay, such as the player’s health, damage, and stamina, at the start of each level.

The AI Director will deploy Corruption cards against the player in addition to player cards to hinder their progress. However, for beginner players, Turtle Rock has created a Classic mode, which is a more accessible game that removes all of the cards.
The developers of Back For Blood are the same that brought us “Left 4 Dead” and according to them the new game will have a more expanded story line and will have “a more uplifting tone than other zombie games on the market.” The players aren’t just trying to stay alive and find safe areas. They’re battling zombies in order to build safe areas.
According to the game’s creative director Phil Robb, the “Cleaners” will be more confident and capable than the “everymen” from Left 4 Dead.
So all in all it looks like Turtle Rock went and did their research as well as working hard behind the scenes to bring us positive changes that will go into Back For Blood.