When can we start adding the sisters tag to pictures that feature these two? I mean, obviously, we can't tag every picture of these two as "sisters" at this point, but what pictures can be tagged as such (provided that a spoilers tag is added as well, if it is not present already)?
Please remember to cover up comments that have spoilers in them. I went ahead and edited your message to cover up the spoilers.
As for your question going by topic #10311, the answer would seemingly be we don't tag tags like the one you're asking about if it would be a spoiler. For images that explicitly mention it (such as in text), then just using the spoiler tag is sufficient.