I'm sure an alternative communication method could be established if the sibling tension is quite that bad. They must have some method of doing so now, even if messages between them currently have to go through 3 people, 2 computer systems and a partridge in a pitstop topiary bush.
Maybe it is too much to hope for that Claire and Jonathan can have a good relationship with each other, but that's no reason not to use their respective talents fully. Come on, lack of appropriate imagination looks like one of Williams' problems at the moment - some better-focused imagination could spark off something worthwhile.