In hosting the Creative Brief the client is granting the Talenthouse artist community permission to use the client's branded elements, but the client retains ownership of these. Typically Selected Creators are granting the client full rights, or an exclusive license to the artwork in exchange for the Creative Brief incentive. Due to this license, the Selected Creator may only be able to use the selected work in their own portfolio (and not license it to any other party during the license term purchased through the Creative Brief).
On 99% of Creative Briefs, all Non-Selected Creators retain ownership of the original portions of their work, i.e. what they created originally. The Creator cannot sell on work that contains Intellectual Property of the client (logo, product etc), as they don't own the rights. But in theory, yes, a Non-Selected Creator could remove the branded Intellectual Property elements and sell the artwork under a different license agreement.
Some Creative Briefs request Creators don't share their submitted work anywhere because of the content, or due to how the client intends to use selected work from that campaign. Some Creative Briefs encourage all participants to share the work even if it includes brand Intellectual Property. If there are restrictions, it will be detailed in the Creative Brief guidelines.