Thanks for your reply.
As regards the Council land, as the ROW has been extinguished, none of you have a right to use it unless the Council are prepared to grant a new ROW to one or more of you.
As a ROW "attaches" to a property, it is up to No. 75 to approach the Council in this regard and try and agree on what lump sum, if any, needs to be paid to the Council and the amount of maintenance charge, in return for the Council granting a ROW. These amounts, like in the past, are going to be very much at the discretion of the Council, as they own the land and can therefore demand whatever sums they think No. 75 will be willing to pay.
A local search will only reveal what land is adopted (ie maintained) by the Council. If you wish to establish if No. 75 has already been granted a new ROW, you would need to do a search at the Land Registry. This can be done on line- by obtaining a copy of the Deeds to No. 75 (called "Official Copies of Title") and these will show if the owner of No. 75 has entered into a new Deed of Grant of a ROW with the Council.
As regards the private ROW immediately behind your rear fences, I am not sure if each of you own your own section, but if you do, your Deeds will probably be showing that No. 75 has a ROW over each of these sections. If there is therefore a question mark as to whether you are under a duty to clear any vegetation, the answer would be yes, as you would be under a duty to make sure that No. 75 can exercise their ROW over the private ROW.
I hope this answers your question, and if so, I would be grateful if you could leave positive feedback.
Feel free to ask for further clarification, if need be.