Apple ID

This could end up being a multi part solution. ;-)

This support article instructs as to how to create a new, non-child Apple ID = create an Apple Account. --> How to create a new Apple ID - Apple Support

Merging Apple accounts (IDs) or transferring items is for the most part not officially supported. Read the links below for things you may need to do to transfer as much as is possible and to share some others.

Apps and media bought with one ID are permanently associated with that ID. Typically in a situation where one person is splitting off from a shared ID, the other person is a family member and would use Family Sharing to continue to have access to apps. In a business content you may not wish to do that since one of you would have to guarantee payments by all members with a credit card.

- Family Sharing - What is Family Sharing? - Apple Support

- Set up Family Sharing - Set up Family Sharing - Apple Support

Just buy the apps again.

For sharing material, there are different ways depending upon what you want to share. iCloud Drive is probably the one you would most need.

Share folders with iCloud Drive --> Share files and folders in iCloud Drive on iCloud.com - Apple Support

Read How to use Shared Albums in Photos on your iPhone, iPad, and Mac - Apple Support about how to share photos.

As for keeping what you have now, if you have signed into the first ID on a device then fortunately when you sign out of that ID, do not erase the device, then sign in with a different ID, it asks you in most cases if you wish to merge the data from the two IDs on your device (toggle the ones you want to on). Say yes and later delete individual items from the other ID that you do not want. Note, in How to save apps and progress on one Appl… - Apple Community a Community Specialist says, "you will not be able to transfer the meta data from one Apple ID to another. Once you switch to another Apple ID the information associated with the old Apple ID will be gone except for physical content on the device like photos and videos." Also turn off storage optimization before doing this. With Optimize Storage, smaller, space-saving photos and videos are kept on your device while all of your original, full-resolution versions are stored in iCloud. Make sure photo optimization is turned off. Manage your photo and video storage - Apple Support

There's a lot more I could go into but I think it best you tell us what your needs are in terms of access to material the other has. For example, you could both have access to the same email accounts as well as having your own personal one.

I have left our the larger scale MDM solution. If this is a larger business you may wish to investigate that.

Small business support by Apple --> Business - Small Business - Apple

Intro to mobile device management profiles - Apple Support

Intro to mobile device management profiles

"MDM [mobile device management] lets you securely and wirelessly configure devices by sending profiles and commands to the device, whether they’re owned by the user or your organization. MDM capabilities include updating software and device settings, monitoring compliance with organizational policies, and remotely wiping or locking devices."

You will need to stop sharing apple ids. Apple ids are personal and are not meant to be shared. So either you, or your office manager will need to create a new (business) account for themselves