How difficult is it relative to Engineering maths?
I'm not really familiar with engineering maths but I'd guess that it's at least on par. Though the two use pretty different branches of maths.
Do most people who take the course pass?
Pass sure, but if you want to pursue actuarial as a career you're really trying to get the exemptions for Part 1 from the Institute of Actuaries Australia. Getting an exemption requires a 70% minimum in quite a few subjects found
here.CT1, 2, 3, and 7 would have fairly high pass rates, but CT4, 5, 6, and 8 are much lower, I'd guess around 50%. If you miss an exemption you can take an exam through the institute so it's not the end of the world. Getting all of the exemptions takes nineteen subjects, more than the sixteen commerce units you're given in a double degree, but if you're focusing on engineering as a career then the exemptions are less important.
Is it a heavy workload to taken co-currently with an engineering course?
Commerce in general has a fairly light workload, so despite the extra difficulty of actuarial studies, the workload shouldn't be higher than a straight engineering degree.
How easy is it to transfer to a different major if Actuarial Studies is too difficult?
Pretty easy, a lot of the subjects needed are part of Finance or Econometrics majors.