Our neighbours to the rear of us are selling their house and the buyers survey picked up on a an issue with the boundary wall, which is retaining their land which is about 2m higher than ours.
It has some cracks and leaning. They have had a structural repair which says they don’t deem it to be dangerous, but recommend that it needs rebuilding. They have given an estimated cost of £15-£20k 
Their boundary actually runs along both the back of our house, and our next door neighbours, so the wall is shared by 3 houses.
My deeds say it is a joint responsibility, the rear neighbours are insisting it it ours and next door’s responsibility.
We have legal assistance on our home insurance and are waiting for advice from them but wanted to see if anyone here can help in the meantime.
Our buildings insurance won’t cover it as it is wear and tear.
My questions are - as is stated the wall is not in a dangerous condition, are we obliged to carry out the recommendation to rebuild it? Even if we only end up paying a third, we just don’t have that sort of money - we have a young child and a baby on the way, we don’t have the affordability to take on any more loans or increase our mortgage.
So can they enforce us to repair? And are we likely to be liable for the cost?
Any help appreciated. Thanks.