The client ruler takes advantage of the recruitable general fuction that was introduced with BI and RTW 1.5 (its part of the engine), they aren't part of you family tree so they aren't proper family members.

You can't change a FM's bodyguard using the script unless you make the script kill the FM and then spawn a new one with the same name but with a different bodyguard, the problem is you'll have the most messed up family tree ever. It's quite annoying you can't have multiple different bodyguards but I guess we have to live with it :/.