Rank musical instruments hardest to easiest

They're not, surely. They are included in a wind quintet but are brass instruments.

I don't think that you can really compare - some instruments are easy to start but harder to master. I teach violin (I also play woodwind and piano): it much harder to get a child playing a note on the violin than, say, a piano where they hit a key and the right pitch comes out.

A child can progress to Grade 1 piano very quickly, whereas this is slower on the violin, but the step up to grade 2 is very small.

Loosely, I would say (easy-hardest): percussion, woodwind, brass (including french horns which are technically woodwind), strings.
I say this mostly because the string section always takes the longest to rehearse in orchestras.

I don't play it but I think due to embouchure and the fact the instrument falls apart/ breaks easily. Also there's something strange about the transposition nature of the instrument, resulting in weird fingerings... I'm not overly certain but I'm sure someone else can enlighten!!!

Subjective, but this is what I think; (take this very lightly! - I think a lot of them are equally hard/easy due to different issues - whether you're a beginner or an advanced player, fingerings, embouchure, breath control, temperamental instruments etc)

Organ, Piano, Pedal Harp, French Horn, Violin, Clarsach, Northumbrian Pipes, trumpet, Viola, Clarinet/Oboe (oboe is hard to make a sound whereas the clarinet has horrific fingering patterns), Cello, Percussion (depending on what type?) Bassoon, Trombone, Irish pipes, Guitar, Piano Accordion, Tuba/Sousaphone, Double Bass, Saxophone, concertina, Digeridoo, Scottish Bagpipes, Flute, Ukelele, recorder, Kazoo.

I only know about strings so I would say the cello is easier to start than the violin

Lots of this is personal - some people will find one instrument a doddle, but other people will find it incredibly difficult. And something like the oboe is simpleish to learn the basics but incredibly hard to play nicely.

But the French horn is usually seen as one of the hardest to play, along with the church organ, and the flute and violin two of the easiest.

DS observed that the double bass was very difficult the other day - when I asked him why he thought that, he said "well, the way Bob plays it he makes it sound like it's a very hard instrument to learn"