两个经济担保人选1d, 三个经济担保人选1e. (一个经济担保人选1a. 因为你还要填写I-864A,所以不属于一个经济担保人)
For part 3, question 2, should I check it if Im applying for my mum as well?
Yes.
For part 3, question 7, should it be 2 if Im applying for my mum as well?
Yes.
For Part 4, should I choose 11.a., 11.b?
You should choose 11.a., not 11.b
For part 6, question 6c. Current income - does it refer to annual income?
Yes. write like $999999/annual