Loz2212:
I'm sorry. I'm literally none the wiser. I've zero experience with these whatsoever. I was aware of the mistakes because it tells me about the conflicting declaration at the bottom.. Not because I understand what is happening lol.
Think about it for a little while.
The Arduino has a number of I/O pins. You can't use one of them for two different things. It would be like trying to put your two feet into the same shoe.
And as an extension of that idea you cannot use the same name for two different variables.
The first thing you should do is go through the separate programs and make a list of all the areas of overlap.
Then make changes in two of the programs so that you have three separate program without any conflicting variable names or use of I/O pins. Make sure that the three separate programs work with those changes. If there is a problem fix it before trying to merge anything.
When you have all three programs working without any overlapping usages then have a look at this Simple Merge Demo. And don't try to merge all three programs at the same. Merge 2 of them and make the merged version works before trying to merge the 3rd.
...R