Multiple audio options on a single disc - Possible problem?

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Blu-ray discs have varying storage capabilities depending on the number of layers on the disc (I think typically 25, 50 or 100 GB). Apparently some films are closer to this limit than others, depending on film duration, number of extras and various other factors.

Since some discs contain multiple audio options, I wonder if this is sometimes achieved at the expense of audio- or video bit rate? For example, could a single layer 25GB disc realistically contain an average 2 hour film, some extras and multiple lossless audio options, or should one assume that in such case, some compromises have been made along the way?

Is it even possible to make a rough estimate of how much storage space each individual audio track requires?