Mold found under bathroom sink countertop

[Cali Skier]

We have nice house where tenants found mold in 2 locations.  Well I think its only in one location

Questions... How would you handle the situation below?  I know nothing about mold or repercussions of dealing with mold and tenants.  

1. I am thinking of just replacing the countertop in the guest bathroom only

2. If I need to replace the countertop in the kitchen also I am not going to be able to match what's there, I am thinking of just doing granite throughout the house for $2,500 kitchen and 2 baths.  Its not uncommon for houses in this neighborhood to be upgraded to granite.  But wife thinks it wont attract tenants much

3.  I would like to just go in with bleach myself and scrub it and kill it but wife says these tenants will expect a pro to come in and is concerned about me disturbing it and getting in the air.

4. Is there anything else I should be worried about in this situation?

1st. Guest bathroom.  It appears that the mold is only confined to the underside of the particle board countertop around the sink edge.  

2nd. Kitchen sink, the black eaten away part 7:00 from the hoses coming down from the bottom of the sink.  Tenant thinks this is mold.  There was a leak at that location 3 years ago that I fixed.  I don't know or really think there is mold there.