GET THEM TESTED
If you have taken a DNA test, you can use a Christmas get-together to show your family some of the more interesting finds that you have made, as a means to get them to consider whether they too might be willing to be tested to try to help you out.
While not everybody may be as interested in family history as you are, a fun way to lure them in is to perhaps show them your reported ethnicity results, before you reveal some of the cousin connections and stories that you have uncovered. If family members agree to participate before Christmas, you can even order tests in advance and have fun testing everyone there and then.
There may be questions about privacy and the possibility of hidden surprises, so do make sure that you discuss these with your relatives in advance.