In your position I would do this.
Replace the second junction box with an NTE5a linebox.(If the one in your Hall is this type use it and use the standard extension socket in your room to replace it. You would need a new back box)
Fit a filtered faceplate to the NTE5a linebox.
Connect the wires going to the downstairs sockets to the 2 and 5 terminals of the facepate.
Connect the wires going to your room to the A and B terminals of the faceplate.
Fit a filtered faceplate to your room socket. One of these would be suitable - XTF-68/85 - Pre-filtered Telephone Socket - ADSL Nation
You can them dispense with the filters on your other sockets and would have broadband available from the NTE5a or from the socket in your room.
You would need to buy the faceplate linked above, a XTE-2005 Filtered Master Faceplate - ADSL Nation and one back box.