Here is how I would approach this problem:
1) Have at least 2 people, 3 is better.
one person stays in the upper/farther cottage, on the balcony, or at the windows where the maximum privacy is needed.
the other two walk the land in between the two. One of them holds a stiff tape measure or something light enough to carry, but stiff enough to hold upright. Example: A piece of PVC pipe, with heavy dark markings every foot or two.
2) The person with the pipe walks around pretending to be a tree. The person in the cottage is saying "a little to the right.... " and other remarks. Then, when the pipe is well lined up the people need to know how high a screen is needed at that point. The 3rd person makes a note of the location (place a flag, a rock... something with a label) and makes a note:
Location A- need wide tree. Max privacy starting 6' above ground, up to 20' high.
Location B- A low hedge to screen 3 windows. To 4' high, 10' long.
3) Lay out the cottages and existing features, then add the comments.
Then go shopping.
Notes:
If you need something tall, a tree will leave the lower area open so you can see under it.
A hedge does not have to be a formal, pruned thing. It can be an irregular line or grouping of plants that naturally grow to the right height. If you need a screen that is only 4' high, then do not buy shrubs that grow to 8' That is a recipe for hard work and (often) ugly plants. Get something that grows to perhaps 5', then light trimming every few years will keep it in the right size range.
