Question on elemental weaknesses

Hola!! Need clarification on the following.
I’m under the impression that if an aniimo has dual elements they are weak against both of that elements weaknesses. Additionally I can only leverage and element weakness only when a use the attack with the element is weak against. eg. is is dual fire/dark if both skills are fire it wont trigger elemental weakness against electric type aniimo.

Also do resistant and strong weakness cancel out on dual elements?

Thanks.