A will is legally binding, despite what others may want.....since you are concerned about final arrangements, it should be a simple matter to specify.

As someone who dealt with my father's arrangements, and his wife who did not like what he wanted, Dad put it in his will and that was the end of it. We also had to spend some time researching Catholic funerary practice. Dad was buried at a National Cemetery and she did not want him buried there because she thought it was unconsecrated ground. We had to find the specific canon that addressed burial in military cemeteries.....it was a nightmare.

So having gone through that, write down what you want your final arrangements to be....method and place of burial, memorial or open-casket, music, flowers, ritual words or acts....it's actually very helpful for the survivor's.