Rippers:
The confusing thing on first glance is the wording of "3 instead of 1" combined with "double". But actually it is rather easy:
The toad does not change the attacks characteristic. What happens is:
The Engine doubles the attacks characteristic from 1 to 2.
Now the Ripper makes its 2 attacks.
And while each of those 2 attacks is carried out, you check if the toad is within 2" of the target unit, and then it makes 3 instead of that 1.
I know it is the same result as you said, six attacks.
It is just important to explain it that way so it is clear to everyone why those two rules are working together without conflict.
Kroxigor:
This one is interesting, as there is no numerical value for the attacks characteristic that you can double.
That leads to two possibilities:
1. The dumb one: The Kroxigor's attack is not affected. But why shouldn't they swing twice? Time crawls to a halt so the Seraphon army has a free attack action. I see no reason why the Kroxigor with the Moon Hammer should stand around and do nothing during that time.
2. The reasonable one: You trigger the special paragraph twice. So the Moon Hammer counts the number of enemies within range twice, before carrying out any of the attacks.
So yeah, for practical purposes the Moon Hammer doubles its attacks.