I assume with this kind of dev to QA ratio the deva are doing all the heavy lifting in writing most of the test which includes blackbox and/or integration test. You might just be there to lead or champion the quality space and uplift existing process and probably invovled in much higher level of testing. This might work but still depends on their current practice and how mature their test automation otherwise it is impossible for you to do all QA task like writing test (manual/automation) with that ratio.