Chickens not wanting to stay in the coop.

Hi everyone! I've lurked on here in the informational section but I had a question that I couldn't seem to find the answer to.

This is probably a frequently asked question on here, but after trying some of the methods I have found on this site none have worked for me so far.

I have 8 chickens that I let roam around my house during the day. 2 of the 8 are the first generation of chickens I owned. They are Rhode Island Reds. The last 6 are some new chickens I bought that are a Cornish Rock/Rhode Island Red mixes, or so I was told by Tractor Supply. When it came time for the 6 new chickens to come to the 20x30 dog pen I have wrapped in chicken wire, I built them a separate coop and roost on the opposite side of the pen. I then put the 6 new chickens and the 2 old chickens in the pen together for about a week. After the week I let them all out again and they all returned like normal for a few weeks.

One night I went outside to lock them up and check and make sure they was all there and I found two missing. I later found them up in a tree close to the coop. I got them down and put them back into the pen. The following night more of them was up in the tree, so I got them all out and put them in the coop again. This repeated until they was ALL in the tree, old chickens included. I figured they was getting hot since it was a summer night and left them up there all summer long with no problems. When fall came they kept moving their roost around to the point where I could not locate them anymore and 2 of the chickens disappeared.

I rounded up the remaining 6 chickens and put them in the coop for about 3 days, with no luck. I now have them rounded up again and they've been in the coop for almost a week.

Am I going about this the right way? The chickens seem to all get along just fine, and even some of the white ones will go into the red one's coop at night.

 

I let them out today, if they do not go back in I will round them all up again and leave them in there for a longer period of time. I have not considered giving them treat, but I may start to do it.