Q1 And draw them all along, and flow  To join the brimming river  For men may come and men may go,  But I go on for ever  1. What does ‘them’ refer to?  2. What does the word brimming signify?  3. Which poetic device is used in last two lines? 

Guy, you have written only the half question!
Well, But I've read the poem...So here's your answer.
?Them? refers to the ?lusty trout, sailing blossom, grayling, foamy flake? and ?silvery waterbreak above the golden sand?.
The word ?Brimming? sygnifies that the River is very wide and full of water.
The figure of speech in the last two lines of the stanza is REFRAIN which is used to give the main motive of the poem and emphasize a line.( You can see the line is repeated throughout the poem.)