The system is shown in the attached picture.
If the resistance of the ammeter becomes not null, it must be accounted for when calculating the total resistance of the system.
The ammeter readings are inversely proportional to the total resistance, therefore a bigger resistance would lead to a smaller reading.
The voltmeter readings are directly proportional to the total resistance, therefore a bigger resistance would lead to a bigger reading.
Therefore, if Ra > 0, the ammeter readings decrease, while the voltmeter readings increase.