Lending my own $ to a real estate investment firm (How do I document?)

[Carlo D.]

Hello to the community. I was hoping to get some guidance on how I should structure a certain transaction I am getting into. Here is the background. 

I am going to lend my own funds to a real estate investment company of which I own 50% of to purchase RE. I will be charging this RE investment company (again an RE company that I own 50% of) market interest rates. How, or better yet, who should I go to, to document this transaction? I am not so much looking for servicing the monthly payments, but more of creating the necessary legal documents and filing with the appropriate govt entities so that I can place a lien on the title of the RE that we are purchasing. 

I'm not even sure if I asked the question correctly. I'm assuming I would need to go to a law firm but I am not sure who would provide this particular service. 

Any help and guidance would be appreciated. Thank you.