We investigate the effects of the historical language contact of Modern Greek (MG) with Vlach Aromanian (VA) in bilingual speakers of three generations living in Epirus, Greece. We focus on a VA variety spoken in a specific language community, with our study constituting one of the early attempts in this field of research. (1) Background: Given that bilingualism is a dynamic process in which language domains are not uniformly affected by external (i.e., sociolinguistic) factors, the investigation of bidirectional crosslinguistic influence can shed light on the resilience of morphosyntactic and semantic feature changes. MG differs from VA in a number of morphosyntactic properties at the DP domain, namely definiteness marking, positioning the adjective and gender marking. (2) Methods: To examine the language contact effects in VA–MG bilinguals, we elicited spontaneous language production in VA and MG from speakers across three generations with different levels of proficiency in each language. (3) Results: The data analysis showed evidence of bidirectional crosslinguistic influence since (a) MG seems to affect VA in definiteness marking and adjective positioning in younger bilingual groups and (b) VA influences MG in gender marking in older bilinguals. (4) Conclusions: The present study presents original language data from VA–MG bilinguals and provides evidence of bidirectional language contact effects.