Hi,
In my understanding, only highest degree is required to be assessed.
I got only my masters degree assessed and got an ITA and a PPR.
However, that was because my Bachelors college was taking a long time to hand me my transcripts. I believe the fee is same for both one or two degree (you may please double check on that front) so i'd say if you have your documents get the last two degrees evaluated.
Also, as a personal experience, i got mine from IQAS whereas my wife had it done through WES and I'd say WES is better. Result in a month as against 2+ for IQAS.
Good luck!