It seems reasonable to argue in the general study of linguistic transfer that only in the case of multilingualism can one begin to test and understand its real dynamic nature. In the case of L2 acquisition, where transfer has been seriously investigated for decades, complex questions of what transfer patterns might reveal cannot be as meaningfully contextualized to the extent they can be in the case of multilingualism. This is so because in L2 acquisition, transfer either materializes or it does not. When it does, there is no mystery about what the source of transfer is; it must be the L1. However, in the case of multilingualism there exists the possibility of several sources of linguistic transfer. The L2 status factor, the typological primacy model (TPM), and the cumulative enhancement model (CEM), despite important differences, all embrace the idea that transfer in multilingual acquisition scenarios is dynamic but ultimately predictable, and, by extension, logical, based on cognitive factors. This study aimed at analyzing the morphosyntactic transfer of preposition stranding, auxiliaries and SVAO word order in two mirror-image L1/L2 groups of L3 Spanish learners (L1 English/L2 Russian and L1 Russian/L2 English) in the initial stages of acquisition. Comprehension and Production test will be designed to see whether the transfer is facilitative or nonfacilitative to the acquisition of Spanish. Although Spanish and English are close typologically, Spanish and Russian share quite a few structures in terms of word order, conjugation, declension, etc. Results may show that transfer from participants in both groups comes from L1/L2 despite the fact that this transfer is non-facilitative that would support for the TPM. This study will provide evidence for either TPM or other models by combinations of Germanic, Romance and Slavonic languages which is in fact the novelty and uniqueness of this research in order to test the empirical predictions and ecological validity of the TPM.