Go B2 visa interview together?

The first time, my parents went for B2 visa interview together,
but they both were rejected;

The 2nd time, they went seperately. My Father went first and he
got the visa. After that, my mother had a couple of attempts, both
failed on all of her attempts. Later my Father visited me and stayed
for two months;

Now, it is more than a year and half. I'd would like both of them
to go and have a try. But my Father is counted as a visa
applicant who hasn't been rejected, my Mother is counted as one who
has been rejected.

I prefer to having them go for visa interview together.
Can they go for B2 visa interview together?
Should they go for B2 visa interview together?

Thanks a lot!!!