Buying first set of propertys

Two houses next door to the house I live in came up for sale..  we have started the process to purchase them, there are currently two renters there.. and the houses are not in the best shape, the landlord has been collecting rent on the property's for years, and does absolutely zero maintenance to them.. nice slumlord of a guy.. my question is the one renter was complaining to me the other day about a mold issue in the basement, we live in a damp area down by the river.. I was just wondering if this is something a will become legally liable for right away if issue were to arise, I plan on getting the issue fixed asap when I take over, just wondering if it's something they can come for me right away for.. and also what are some good ways to remediate basement mold.. thanks