As for the question "Is it harder to sell 2 homes than 1 home", the answer is, of course it is. Most people, unless they are buying the homes to rent, are looking for one home to live in. It also depends on how your lot will be divided to accommodate 2 homes. Is one home located behind the first home? Will an easement have to be implemented get to one of the homes?
The best advice I can give, is to take your situation to a local REALTOR and get their opinion on the best approach for your property.