It is permissible to offer a cow, however you will have to offer 2 for a boy and 1 for a girl. It would be more economic and closer to the sunnah to slaughter two sheep or goats.

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The marriage is correct but if he doesn’t register you in a civil court, this means he is either married or intending to marry another woman which he can’t do in a civil marriage. He wouldn’t be able to get you a visa as you are not registered as his wife .

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