The ISHS user categories: Institutional and Country/Region Membership, for obvious reasons do not come with membership privileges for individual persons and are equally not accepted for abstract submission in ROSA.
The procedure of entering an abstract consequently the submission of the respective paper and the review process that follows are all part of a highly personalized and individualized workflow involving notifications and messages going back and forth between all parties involved in the process (author, convener, editor, reviewer etc.) hence any shared user account is obviously not authorized neither suited to be used in this process.
To submit an abstract the presenting author must hold or activate a personal user account with ISHS. The user account should be in the presenting author's own name and associated with his/her personal email account.
See also this link for more information.