As mentioned before, travel benefits depends on who your employer is.
In a nutshell: employee and immediate family (wife, siblings, mom, and pop) travel free (depending on length of employment) or at a reduced fee with no limit on amount of travel. Siblings continue to travel free or at a reduced fee until not considered a dependent. The company might also have a “registered companion” type of pass for those who are not married or legally cannot be married. In addition some companies have “buddy” passes which have higher fees and are limited to a certain amount per employee. Each company also decides the rules deciding the priority each traveler will be placed in on the passenger list (dependent on pass type). As far as code share partners it depends on the agreements between the partners. Most code share partners place restrictions on certain family members (mom and pop), “registered companions” and they usually do not extend privileges to “buddy” passes. I hope this helps.
Skyhungry