In-Laws expect elaborate church ceremony....?

I'm getting married in June. For the past 4 months of planning i have dreamed a very simple ceremony in a gorgeous park here in Portland. My fiancee loves the idea of it as do it. My fiancees family-mom, dad, gma and gpa- called today, and began talking about how to decorate the church, what music will be played.. so on and so forth. We tried to explain to them about the outdoor ceremony and its like they do not hear me. They have plans to go and speak with different churches this week. How can it get through to them what i want without hurting anyones feelings?! Help!!