Do these weapons make penalties on the AB as when one uses two weapons? That is, do feats such as dual weapon weilding help when using double axe/blade/mace?

Not sure what you're asking in the first question.

But yes, for question two. Ambi and Two Weapon Fighting helps immensely

Pretty sure they follow all the rules for two weapons. Although im not sure if things like weapon finesse work on them or not

You get a -2/-2 to hit with Ambidexterity and Two Weapon Fighting. The weapons count as light weapons in each hand in that regard.

But cannot be finessed as it is a two-handed weapon.

Thanks!