i think i answered all your questions...
about marriage Cert.. ok, let them bring it.. i don't think it is too heavy to exceed a luggage limit... what's the problem? but i can not see any case when they will need it except of checking in to the Hotel.. since they are staying at your place, and unless you require from them this document, they should be ok...

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“You become responsible forever for what you have tamed”. Antoine de Saint-Exupéry