As a company, if I hire a graphic designer to create ads, brochures, etc who owns the InDesign files? Does the designer or the company that hired the designer own the files? My company hired a designer to create some sell sheet templates and now he won't give us the InDesign files claiming intellectual property.
Depends on what the contract says. Typically the freelance designer owns the source files and will deliver you a finished version for you to use, example a PDF for print.
If the designer works for the company then the company would own the source files. All this really depends on what the company and the freelance designer agreed to.
If you're wanting the source files I would contact the designer to see if you can purchase them. Based on what you've said it appears your company hired a designer for designs, they delivered possibly a PDF and now your company wants everything associated with them. Think of this scenario like you hired a welder to weld some metal and you now expect his jig and welder. That's not what you purchased you purchased what he made with said items. That designer could have paid for fonts you dont own the rights to use even.