We have covered the purchase requirements so far.
Transportation: In MO, if you are over 21 and can legally own firearms, you can carry a loaded and concealed handgun, or rifle too, I suppose, in your vehicle, even if you are not a MO resident. That's how we got car carry and ccw in the first place.
Now, I'm not sure what you're trying to accomplish. If you're coming in to visit your brother and get him into firearms...well. You should be able to bring whatever gun with you, no problems bringing it into MO. If you want to buy one....well, now that gets complicated. YOu can buy one, but it will have to be transferred back to Cali, and then you know all the stuff involved there. Your brother can buy one here, but then he has to do the PTA, which depending on which county he is in, could be a few minute wait, to a full week. If he's in St Louis..well...good luck getting all that done in a week!
So, depending on what you mean by getting you brother into guns, it might be best to post where you are going to be in MO or KS, and when, and then maybe some of us MO-KS residents can work with you, meet up at a range, etc. Either way, we need a little more info about what it is you're trying to do here...