The Competition Model proposes that sentence interpretation relies on cues such as word order and verb agreement, weighted by their validity, cost, and strength. Heritage bilinguals offer an especially informative lens for this framework because they access multiple cue systems and vary widely in language experience, proficiency, and societal exposure. This study examined how these factors shape sentence interpretation in 49 English monolinguals and 52 Spanish–English heritage bilinguals using a sentence-interpretation task in English and Spanish. Results showed that bilinguals adapted cue strategies across languages, relying more on verb agreement in Spanish and word order in English, consistent with patterns of amalgamation and transfer. Processing costs increased under cue conflict, reflected in longer response times, particularly when bilinguals engaged morphosyntactic cues in noncanonical structures. Objective proficiency demonstrated language-specific effects in English: English vocabulary and bilingual listening comprehension predicted greater reliance on word order in English. Whereas objective Spanish vocabulary and self-reported Spanish proficiency predicted stronger agreement-cue use in Spanish. Bilinguals exhibited diverse cue-dominance profiles, highlighting substantial within-group variability and extending the Competition Model through composite measures of cue strength.