Most Tax Effective Way to Purchase This Storage Facility

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I have a storage facility that my husband and I likely are going to be purchasing. The owners are my husband's grandparents and they are willing to work with us to make a deal that makes sense for everyone.

This is the first time that I would be purchasing a property from a family member so wondering if there is a more tax efficient way of doing this deal than a straight sale? 

They are also willing to finance the deal and likely for little to no interest. Wondering what the benefits would be to them, if any, on doing a zero interest loan for us.

Sorry for not having a ton of details here, this is the first non residential deal I'm doing so not entirely sure of what questions to ask.

Thanks in advance.