We recently put 2 metal curtain rails up but due to the length needed, our best option was to go for extendable ones (or so we thought) We have metal curtain rings on as well but when you go to pull the curtains the rings all get caught in the join btw the inner and outer rail. This means every time the curtains are pulled each ring has to be individually lifted over the join, and considering there are 2 rails at almost ceiling height, and I'm not very tall, this is a bit of a pain!
You could try two seperate rails with the support in the middle. The curtains then get drawn to the middle.
Either that or as I have done in my daughters that has a long rail, I fixed the curtains to the rail so they don't draw back but open out and tie back. If you imagin the way children draw a house with curtains at the window!!! I know in a 5yr olds bedroom it looks cute but might not be appropriate for a sitting room though.
OR try covering join with matching duck tape . This lessons the step . And you try a little silicon spray wiped round inner of rings to make them slide better.