Neighbor Doesn't Agree with Boundary Survey after 20+ years of mowing. Possible Adverse Possession case?

Hi,

My question takes place in Maryland. I moved into a house earlier this year. The neighbors to the right have a house set back and at an angle to the street. After moving in I had a boundary survey (neighbor to the left has a fence 3 feet over property line so was trying to get that resolved). After the stakes were put up, the neighbor on the right mowed a good 20 - 30 feet onto my property (this was their first mow of the season). One day, in April, I asked the wife if she realized the stakes were the boundary. She was almost immediately defensive stating that can't be right and that she could go get her plat. She said they had always mowed there and had a jungle gym for the kids in a bare spot in the yard. Then she jumped to, I don't care keep the trees. Taken back and trying to be neighborly I told her I was trying to figure out where we should mow to. Again trying to be neighborly I suggested we mow to a spot half way in between where they have been mowing and the property stake. The husband then came out and looked at the marker. The husband said, whoever gets to it first cuts it. I agreed though that is not really what I wanted to have happen but I was trying not to make enemies on both sides of my house.

Should I be concerned that they can take my property through adverse possession. Looking at historical satellite images, the trees have been there since 2007 which is not enough time for adverse possession but the jungle gym (which is straddling the property line) has been there much longer and they claim to have mowed since they've been there.

Edit: Sorry, i forgot to mention that they have owned the house since it was built. They have definitely lived there for more than 20 years.

Edit 2: I was exhausted and pretty upset when I wrote this. I also left off the fact that they had planted trees on what they thought was their property. That is what the neighbor meant when she got defensive and said keep the trees. As stated the trees were planted in 2006 or 2007.