"This is a picture of our 6-month-old LeoBerner hybrid. The father is an AKC purebred Bernese Mountain Dog and the mother is an AKC purebred Leonberger."
The LeoBerner is not a purebred dog. It is a cross between the Bernese Mountain Dog and the Leonberger. The best way to determine the temperament of a mixed breed is to look up all breeds in the cross and know you can get any combination of any of the characteristics found in either breed. Not all of these designer hybrid dogs being bred are 50% purebred to 50% purebred. It is very common for breeders to breed multi-generation crosses.