Here are the actual notes a Highland bagpipe plays, followed by the name pipers call the notes
sounding pitch > piper’s name
A flat > “low G”
B flat > “low A”
C > “B”
D > “C”
E flat > “D”
F > “E”
G > “F”
A flat > “high G”
B flat > “high A”
Pipe music should have a key signature of two sharps, but it’s common to leave this off, and pipers read C and F as sharp whether or not the key signature is there.
I’ve played many church gigs over the years, many pieces arranged by people like yourself who aren’t all that familiar with the instrument. Writing the music correctly is only one of many aspects you should be aware of. Some of the other things are:
-Highland pipes are loud. When the piper starts playing he often can no longer hear the choir or organ. It’s best when the organ is inherently loud and the organist pulls out more stops than they’re accustomed to. Few are the organists who play loud enough to balance with the pipes. Since the piper can’t hear anything but himself complex arrangements can be a train-wreck. Many pipers have never followed a conductor. So, what works best is if the piper can play a straightforward melody or part which isn’t interdependent on what the other musicians are doing.
-The standard pitch of Highland pipes is a quartertone between B flat and B natural. For playing with the organ (unless it’s electronic and can pitch-shift) you need to find a piper who owns a chanter which plays at Concert Pitch. Different makers call these different things such as “466 chanter” “B flat chanter” “orchestral chanter” etc. Only a very small percentage of pipers have the know-how and equipment to play in tune at Concert Pitch. Most pipers don’t know what “concert pitch” is.
-Pipers have to first ‘strike in’ the drones, then bring in the chanter. If your arrangement requires the chanter to suddenly start and stop you might be in for trouble. Musically astute and skilled pipers can ‘cut’ the chanter in and out at will, but most pipers are used to the normal strike-in, and playing continuously until the end of the piece. You can have the piper plug off his drones, but most pipers have a hard time controlling the chanter without the drones. So, the best arrangement is one that allows the piper time to strike in the drones, and then play the chanter continuously until the end of the piece.
It’s quite frustrating to try to perform a piece that’s arranged by someone who doesn’t understand how pipes work and what pipes do.
Here’s the popular piece Highland Cathedral. This pipe band maintains a set of concert pitch chanters and is accustomed to doing church gigs. Still, their chanters aren’t nearly as settled as they would be if they were playing at the normal Highland Pipe pitch (around A=452).
https://www.youtube.com/watch?v=j_vdM5YF6Tc
BTW my avatar was taken when I was playing this piece along with a large professional brass ensemble. My pipes were going well in concert pitch; I do loads of these gigs.