stolen trees

Let me fill you in with the history first then I'll ask the question.
My wife is the oldest of 4. she has 2 brothers (I'll call them brother#1 and brother#2) and a sister. They lived on a farm with over 600 acres. Her father owned 1/2 with another person. When my wifes father died he left each of his children 1/4 of his half of the farm. He leaves all the equiptment and cattle to Brother#1 also. Shortly afterwards brother #1 comes up with enough money to buy the other half of the farm (he never worked a meaningful job). Some years pass and my wife wants her percentage cut off the farm. It takes 7 years to get the surveyor to finish the survey (surveyor works with brother#1 who is now an appraisor) Brother #2 refuses to sign the papers for the split of the farm unless we build a road acroos our land and grant him right of way so he can build his dream house. Brother #2 bought the land from my wifes sister so now he has 80 acres adjoining our 40. My wife agrees because we were able to divide our land into 4 lots and we would need a road for the subdivision anyway. It's a gravel road wide enough for 2 cars can pass and the trees were cut back to 15' awy from the road, all expenses paid by us and road is entirely on our property. Anyway, last year I was walking our property (all hardwoods) and I notice about 12 trees missing in the middle of the woods (about 2 feet in diameter) I questioned her brothers about this and they say they needed to cut firewood for their mom. Now remember that brother#1 has over 1200 acres now and brother 2 has 80 acres surrounding his house and their mothers also. When I ask them about this they tell me our trees are easier to access. We told them they can use all the trees that were cut down to make the road and under no circumstances will they get permission to cut down trees. We know for a fact that both brothers are using the firewood to heat their houses. We put up barbed wire where they were accessing the woods from the road so now thy are cutting trees along the road.

For the last ten years we have been cutting down a Christmas tree on the farm (we always asked brother#1 first since the right trees were on the cattle part of the farm, even though at that time my wife still owned a percentage of the farm) Last year brother#1 told us we could not cut down a Christmas tree. So this year we go to the farm (we live about 70 miles away) to get a christmas tree (neighbor gives us permission to get one off his property) and as I am walking down our road I see that 2 trees about 2' in diameter and 1 that was about 3 1/2' in diameter have been cut. We were at the farm 4 weeks ago and brother#2 had no firewood and the trees were there. Now both brothers and their mother have lots of wood. My wife was furious and asked me to call the sheriff to see what can be done. The sheriff told us that since we have not given them anything in writing that nothing can be done. So now my wife is typing a letter telling them that they will be considered TRESPASSING if any more trees are cut. So my question to those of you who have read this far, "what else should we do?"