I want to say "it depends".
If it's an older receiver that uses a legacy LNB, and the DirectTV dish is using an older LNB AND your relatives only want programming from 119° (most of AT100 and 200), then yes it will work.
However, Dish Network dishes and LNBs to get both 110° and 119° for complete packages and more options is rather inexpensive and then there will be no doubt that it's compatible.
See ya
Tony