Should I have my partner write my letter for my DTV, or should I draft it as an employee of my own business?

I have been asked to provide this for my DTV.

I work alongside my partner as a freelancer/admin role on a self employed basis- has been part time but will be full time when I arrive (remote role)

I also have my own business in the uk which will have income coming in from outsourcing my work.

Do I get my partner to write this letter or do I write this letter as an employee of my own business in the remote role.

Any help is much appreciated

Thanks