Is sibh pronounced (English) shiv or shoo? I've heard it both ways in this Unit.
Both ways are correct. Different accents :)
When do you use "is" instead of "agus"
Using 'is' instead of 'agus' here is marked wrong... can one not use 'is' is in this context?
'Is' will be accepted here.
Okay, we've just had four or five examples of x is y, where x and y are people. Now we're back to x agus y. Why?? When is is appropriate, and when is agus?
You can use either. Use whichever flows better at the time.