Confusing Mandarin drakes in eclipse or are they juveniles?

During early June I went on one of my visits to Barnes Wetland Centre.  In the captive part of the Centre, I came across a confusing selection of fancy waterbirds, including several Mandarin ducks.  One is definitely a drake, as it still has it's distinctive rust-coloured mane and, in the photo below, appears to be quacking at the others who are sharing it's section of the pool.  The two at the top left and top right of the photo are, I believe, also Mandarin drakes in eclipse plumage - or are they juveniles or is the one on the left a female?

I think that the two birds with the green feathers on the back of their heads, and with their backs to me, are Wood ducks and that the one in the centre on the right could be a Baikal Teal.  Please feel free to let me know if you think that I am wrong.  The plainish brown duck in the centre could be almost anything, as far as I am concerned, as I find it very difficult to identify it from the angle it is standing.  I am fairly new to birding and am learning a lot from other people, the internet and a large collection of bird books that I seem to have bought over the last couple of years - some new bird guides, some for their great photographs or drawings and some interesting vintage ones.

Anyway, I do know that a Mandarin drake in breeding plumage looks very magnificent and impressive.  This one must just be starting to go into eclipse as it is looking a bit scruffy - which is not what Mandarins do!

Here, there is Mr Scruffy at the bottom and Mr Even-More-Scruffy at the top of the photograph.

This is a close-up of the very scruffy Mandarin drake - is it an adult in eclipse or a juvenile Mandarin?  I just don't know sufficient facts about them and I am trying to learn.

 Again there is a more-or-less still colourful Mandarin drake and he is with a duck that I assume was a female - or is it another drake in eclipse or, again, is it a juvenile?

This close-up view is, once more, a view of either a young Mandarin or a drake in eclipse - but which one?  I know they start to look more like females when they are in eclipse, but still have red beaks.  Could they be a family of Mandarins - male, female and juveniles?  I am confused!

The photograph below definitely shows a female Mandarin duck.  The photo was taken in May in Hyde Park and she was with her partner and youngster at the time.  This female as a dark beak, not red.