Just to give context, he helped me set up this account, so sometimes I assist on his. It's not very often, but happened last month and caused this issue.
I think at the moment it's better to unsuspend both and agree to not login on his account anymore. Don't want to mix things up before properly discussing it.
It's an interesting idea to combine the accounts. If we decide to merge, can we do it in plesk ourselves or there are additional procedures?