Usually the HOA fees vary depends on the property size - if one unit is bigger than other , that will reflect in the monthly fee. To be more specific what is included in said fee I will need the property addresses.
Let me know if you would like to assist you further.
I would contact the HOA for that question. Some states (such as CA) have other taxes included based on the sales price of the house (ie. Mella Roos... Hope I spelled that right). Some foreclosed homes have "delinquent fees" that were not paid, which the HOA may be trying to recoup.