My guess is that all "liability" associated with the colonial possession of land would have been passed on to GoK around independence; so it is not clear where these folks think they are going with this one. One can look at, for example, native-land cases in Canada, Australia, New Zealand, etc., where legal cases have been against the government of the day and not the British; a judge in the UK will be cognizant of such cases. Have the RV people tried suing (in Kenyan courts) either GoK or the current occupiers of the land?
The "inspiration" from the Mau Mau case seems misplaced. Even setting aside current views and laws on torture all over the world, it would have been hard to sustain a claim that torture by, on behalf, of a government in one country would have been passed on to a government in another country, unless the latter was somehow involved, which was not the case for GoK. That is, the Mau Mau could not sue GoK for torture by the Brits. On the other hand, regardless of what one thinks of such arguments, some can certainly be put forth to the effect that the "illegal" acquisition of land somehow benefitted the natives.
What's more, even without getting into the "merits" of such the case, considering what the British got to with land all over the world, it's hard to see a British judge opening a can of worms that would have the British paying through the nose all over the place. Could the Brits, then, be sued in an African court? Around 2004, some folks in Uganda went to the High Court there to sue the Brits over all sorts of mischief associated with land. I no longer recall the details, but they did not get very far: a couple of the Ugandan judges quickly found out that the Brits had entered into all sorts of tricky agreements with the locals, and they pretty much killed the case. Here, we have a county or two setting off to sue the British government.
Has the Attorney General of Kenya given any legal opinion, or even made a comment, with respect to any applicable legal agreements (between the locals and the Brits) and on independence and (between the Brits and the incoming of GoK)? It is such that will determine where this goes; merely insisting that folks were screwed will not suffice, even if they were indeed screwed.