You can either treat as one, or split and treat each separately.
Overall, I would recommend you treat each one separately splitting things such as your property taxes, mortgage interest, insurance, etc. between the two. Can make things easier to deal with in the future. For example, what if for some unforeseen reason you need to move into one of them and make it your primary residence? What if one of them burns to the ground? Easy to deal with if each property is dealt with individually from the start. A real PITA otherwise.
