As a bit of a background to this problem I'm a student at a university who is currently taking their capstone course for graduation. This issue in particular was raised by my product owner in regards to their wordpress sites.
Currently the way their wordpress is set up is that they have two single sites: their main homepage and another page that they've installed an auction theme on. Both of these instances have their own databases.
What the website owner wants is to be able to take the information from one registration (user completed form) and send the information to BOTH of the databases.
I've sifted around the plugins for database controls for wordpress sites but have yet to find anything that seems like it would accomplish what my product owner would like to do. Since my knowledge of wordpress has been limited until this course, I'm wondering if someone else has a solution to this problem that I've been unable to locate. Whether that be a plugin that has already been created or the correct way to approach creating a plugin that has the proper functionality.
Additionally, my product owner is wary on going to a multisite design. A solution that can be used before going multisite would be preferred but if we have to go multisite to accomplish sending the information to both databases then we will.