The things they teach you in vet school

"When introducing adult animals into a new household be prepared for stress and disputes. The best you can hope for is bare tolerance. Introduced animals will probably never actively seek out each others' company.

Each animal will also like their own space, and will need separate beds spaced well apart to reduce tension. Pets are very unlikely to ever share beds without a fight."

When we introduced all our various fully grown cats and dogs in order to co-habit this house we didn't know any of this. Luckily neither did they.