I created my Lights for the player houses and they're a hit, but I have people asking me if I can upload just one mod for all three homes to Steam and Nexus.

I haven't a clue how to merge these unless I start from scratch. Is there an easy way please?

Those look like all exterior mods, right? I would use TES5Edit to do it. I'm no real expert on using it, but I have used it to merge some cells from one mod to another. Backup your files first. Set the load order of your mods so the file you want to merge into is below the file you want to merge from. Open them in Tes5Edit and find the cells you want to merge under Worldspace. Select one at a time, right click on the top level of the cell in the list it and choose Deep Copy as Override, I think that is right, and then choose the file to merge into. When it asks if you want to make the "copy from" file a master of the "copy to" file, say yes. That should get it done. Copy each cell you made changes in. they will all be listed. Assuming each house sits in one cell and all of your work is in those same cells, you will only have the two cells to copy. Also copy any object resources you may have created that might be unique to one mod, like custom lights or such. You can select the entire category (like, Lights, Containers, NPCs and such) and copy it if you want to.

Once you are done with the merge, exit Edit and it saves your modified file. The one thing left is to remove the master dependencies. There should be two, one for each of the files you copied from. Open, the CK and select the new merged file in the Data window. You will see the two extra masters in the window on the right. Select the two xtra files in the Masters list one at a time and hit Ctrl- delete to remove them and you should be done.

Good luck. Did you remember to make backups? Things can go wrong from time to time, as you may already have noticed.