A client has two rental incomes attached to one property and two debts, but what I add an action to sell the property I can only choose one income and one debt. Is this right?

Yes, currently when the Action 'Sell a property' is chosen there is the option to choose whether an income and a debt are going to stop as a result of this sale.  

This will be changed in a future release. For now,  just add one debt and one income to the action and if the potential date of sale is known, is to record the additional income/debt records with an end date of this potential date.