How to share a 50% of royalties on form 1099-MISC or do I divide it myself?

If you received 100% of the royalty that also belongs to someone else, you will need to nominee them their portion.

Nominee returns. 

Generally, if you receive a Form 1099 for amounts that actually belong to another person or entity, you are considered a nominee recipient. You must file a Form 1099 with the IRS (the same type of Form 1099 you received).  You must also furnish a Form 1099 to each of the other owners. 

File the new Form 1099 with Form 1096 (this is a transmittal for the 1099) by mailing to the Internal Revenue Service Center for your area (provided on the Form 1096).

• On each new Form 1099, list yourself as the payer and the other owner, as the recipient. On Form 1096, list yourself as the nominee filer, not the original payer.  The nominee is responsible for filing the subsequent Forms 1099 to show the amount allocable to each owner

Form 1096

Form 1099-MISC