The first thing to look at in a landlord-tenant dispute is the terms of the written lease agreement. That should specify damage and wear and tear issues so the ladies should take a look at that. Absent a written agreement, then you go to Florida landlord/tenant laws. Factors to consider is that this is not intentional damage and would it be reasonable for someone to do their nails around a bathroom sink with fingernail polish remover. Different countertops have different properties such as granite, marble, corian, laminate, etc. that all have different reactions to different chemicals and cleaners and did the landlord leave specific written instructions about his particular countertop (For example, marble can stain easily). There is a strong argument that this could be normal wear and tear although some landlords will disagree and some tenants will agree. They could spend a day in Court at trial arguing about it. The landlord would need and have to pay for an expert witness to verify his damages.
On a practical note for a lawsuit, the absentee landlord lives in Honduras and would have to travel to Florida or maybe Canada for his lawsuit and comparing the cost of the countertop versus the cost of travel, expert witness, attorney fees, and lawsuit costs, makes a lawsuit economically unfeasable. Further the renters live in Canada and good luck getting a valid service of process on them in Canada. It's a big problem around here trying to collect rent and sue when renters skip town much less when they skip back to Mexico. In my opinion, I don't see this case ending up in Court. A prudent landlord will have a very specific lease agreement and collect a damage deposit, cleaning deposit, etc. up front to cover those things. He would also want to have a local agent to handle all these things which may be a possibility since this is a condo rental but a local agent hasn't been mentioned. This is my 2 cents worth.