I was hired by my sisterinlaw to work for their S Corporation. I was going to get an FSA dependent care benefit but was told that’s not allowable. Is that true?

One company was going to set this up but another, when I called for a second opinion they told me since I was a sister in law I couldn’t get FSA Dependent Care. Is there any way around this? I don’t own any part of the company (stock / shareholder). I also can’t find much information on it and most places I call tell me they aren’t sure what I’m talking about. I’m looking for some clarification.