The most appropriate option to fill in the blank is giggly.

The sentence is about the effect of funny stories on the speaker and their brother. The word "giggly" means to laugh or chuckle in a silly or nervous way. It is the most appropriate word to use in this context because it describes the reaction of the speaker and their brother to funny stories.

The other options are not as appropriate.

• Conscious means aware of one's surroundings or one's own feelings. This does not make sense in the context of the sentence because funny stories do not make people aware of their surroundings or their own feelings.
• Determined means having a strong will to achieve something. This does not make sense in the context of the sentence because funny stories do not make people determined to achieve something.
• Gritty means tough and determined. This does not make sense in the context of the sentence because funny stories do not make people tough or determined.