I have huge sympathy for your friends. I have heard of similar situations, and it seems so unfair. Furthermore, if they used a lawyer when making the purchase, why was this not discovered earlier? Who was protecting them?
The application of laws governing bars and cafes etc. seems to be very random. Why does one bar have to install disabled toilets, soundproofing, double doors etc., when the other bars (sometimes even next door) do not have to? Also unfair, and does not reflect well on Spanish bureaucracy.
In this case, clearly the landlady was well aware of the situation, even during the previous owners time, so one would assume that it was her who initiated the original project, but never completed it. So, one has to ask the question, did she simply rent an empty business local, or did she at some point "sell" (
traspaso) a lease on a fully fitted & functioning business? If so, in my opinion, I would think the responsibility should be hers, to finish the project, as she knowingly sold a faulty product, so to speak.
On the other hand, if she is basically just renting the premises out, and the fixtures & fittings etc. were installed by the original tennant, who have subsequently transferred them to someone else, then I don't understand why she would care if the project is completed, or if the bar gets closed down. She will still charge rent, after all. So why is she pushing them to do it?
It may be worth getting an independent quote on the work, to see if she is just trying to line her own pockets. (Soundproofing a bar ain't cheap, though).
I'm not entirely sure why the landlady is so anxious for the work to be done, but maybe it is because she fears if the bar is closed by the council and your friends are forced to walk away due to lack of funds, she will then not be able to rent it to anyone else unless she does the work herself. So perhaps a compromise could be reached that would benefit all.
Perhaps the landlady could arrange and pay for the necessary work, and a new rental contract could be drawn up, whereby the tennant pays an increased rent for a period of time, which will eventually cover the cost incurred; or perhaps an agreement could be reached to split the cost.
These are just my own thoughts; I'm not a legal expert by any means, and maybe Maria or someone else will be able to offer more suggestions or advice. I hope this may help a little, and wish your friends all the luck in the world. The bar business is tough enough without this kind of headache. I have heard of so many previously strong relationships that break up due to the stress of trying to successfully run a bar here, so the best thing you can do for your friends in the meantime is to remind them that
nothing is more important than their love & support for each other, and that no problem is big enough to cause any kind of damage to the family.