
I to have a blind spaniel - springer to be exact. She is 15 years old now, totally blind, and gets on very well with the other two dogs. She was starting to loose her vision when we introduced one dog. The dog we introduced was a calm one (although a rareity in the breed she was lol) so they get on good.
The other one was introduced about a year ago, when my spaniel was completely blind. The pup was NEVER allowed near the spaniel, unless very controled on leash.
The three live together quite peacefully, and we rarely have problems (other than the blind dog stepping or jumping on the min pins by mistake).
You gotta be careful, and introduce the new pup slowly. You do not want to put them together and "let them be". Have the new pup on leash at all times, when around the blind dog. Teach the pup how you want it to behave, and it will be a ok thing.
When I read your story, I thought, ok this could be my life written on here lol, as it is so similar to my situation a year ago, and then 4 years before that.
Good luck