Unfortunately, there is currently no elegant way to resolve sequence members via the API, as I have already noted to Mapillary developers. For now, hope and patience are our only chance.
Since API v4 is geared towards sector based processing you can try to first manually determine the position (as in a bounding box) of sequences/imagery you are interested in and then download all imagery and metadata in those sectors (or bound box), so that you can match all metadata to all the imagery, and finally filter only those images/sequences that you are really interested in.
However, if I recall correctly, you can resolve sequence members per user. In other words, you can get a list of all the sequences of a user with the corresponding image keys per sequence. So, if you know what particular users or sequences you are interested in then you could take that route. Or, you can go