A few questions about japan ?

For the 1st question I don't think girls can get married at 16 I'm pretty sure they have to be 18 same with guys. For your 4th question I think males have to be 18. And yes I think that step-siblings are okay to get married which actually makes sense because it isn't like your bound by blood you might as well be really good childhood friends. Now for the 6th question I haven't heard anything about it being okay for s to get married but that might be okay.