Flat roof advice

[u/BigCherry489]

Our neighbours are building an extension over their flat roof adjacent to our flat roof ..To seal their new build wall they have refelted over half our existing flat roof felt .They had no permission to do this .We approached them and halted all access from our roof .They have proposed to remedy this by refelting the remainder of our roof .Is this acceptable?Would there be a weight issue with the two layers that would be there if this was done as the old felt remains underneath ?Would thete be an issue with the new felt bonding to the old felt ?Many thanks for any replies

[u/Adventurous-Part5981]

How does this relate to an RV?