We flip houses. Owe investors interest from sale of house in 2018. Won't be able to pay the funds to til 5/15/19. Put expense of interest in 2018 but 1099s in 2019?

We buy, rehab and sell houses under an LLC.  In 2018 our mom and aunt invested with us to get another property.  We sold the property but didn't have the funds to pay their interest.  Being family, they are patient with us:)   I had reported the interest expense under the property that they invested in and that we sold in 2018.  Since they are not paid yet I was planning to create their 1099-int in May of 2019 (when they are getting their checks) but just realized that this might not be the right way to file.  Pretty new to this and am making some rookie mistakes.   I did file an extension for the LLC and my personal taxes.

Any help would be appreciated.   Thank you!