So in my head canon there are a couple of friendships here.
Gordon And Boco:
Ever since Gordon thought he was saved by Boco when Bill and Ben tricked him. He never been mad at Boco. Boco is already friendly and the two engines became friends.
Henry And Bear:
Ever since Henry helped 199 and 7101 (Bear) during Henry's breakdown the two became friends. Henry and Bear are always like best friends to each other as they defend each other in each conversation that others call them bad.
Edward, Bill And Ben:
Ever since Edward keeps Bill and Ben in shape and being like a father figure. Edward keeps Bill and Ben in check and helps them after they get in trouble with The Fat Controller or Sir Topham Hatt.
Percy And Daisy:
The two are best friends ever since Percy has had his incident with the trucks and when he was at the works he'd saw Daisy coming in once every day to check up on him. The two became more close to each other.
Donald And James
Donald and James have been friends ever since the incident of the break van. After the break van smashed into pieces James needed therapy, and still does time to time, but Donald stayed by his side with him as he wanted to help the poor Red Engine. Ever since they always are friends with each other.
Duck And Douglas
Ever since the play of Donald's Duck Douglas always talks about it and Duck always likes it. Douglas becomes jealous of it and tries to do things similar like it. Duck keeps helping Douglas from going mad when he tries to copy Duck and they become friends.
Oliver And Salty
From time to time Oliver had to go to the Docks to help out and always see Salty there. Oliver likes listening to his stories which are always fun. The two become friends while Cranky stays Cranky.
