The word "I'll" does not have comparative and superlative forms, because it is not an adjective. "I'll" is a contraction for "I will". The word "ill", however, is an adjective, and the comparative and superlative forms are "more ill" and "most ill".
Comparative and Superlative forms are for Adjectives and brightly is an Adverb, therefore there is no comparative or superlative for brightly. The forms brighter and brightest exist as the comparative and superaltive forms of the adjective bright.