Dual citizen of Hungary? Living in both Buda and Pest? :P
I would suggest to pick either 'he' or 'she' here. 'They' may be a good option for gendering reasons, but it's grammatically very awkward since it's a different grammatical person. And I think we're already busy enough with all the different forms that translate as 'you' in English.
"They", used as a gender neutral third person singular, is not yet standard English usage, although it may become so as time goes by (and arguably should).
I don't think the Duo folks can be expected to OK it at this stage. The Hungarian ő simply has no single word equivalent in standard English, and in the absence of context you just have to choose he or she at random.