Let the main booker add companion details during the online check-in process
I understand how nice it is to collect more email addresses from guests, but the workflow to add companions during the online check-in process is causing most guests to not finish it.
We (in Austria) require a name, nationality and date of birth of every companion.
During the process, the main booker fills out his/her details, which is working very smoothly. Then the guest is asked to add companions. The guest can add a name and an email address for the companions, who then have to perform a seperate check-in process. This often does not happen, as the guest feels it is too much effort, or the companion is a child and doesn't actually have an email address. Which leads to us having to perform a manual check-in on arrival anyway, and the guest is annoyed because they feel they made effort to avoid just that.
I think, an option to add nationality and dates of birth in the same box where the main booker adds the companions would solve this issue.