If you are filing married filing jointly then you can select that the kids lived with you all year.
If you are legally separated then there is the option that the other parent can release the dependent for the Child Tax Credit. Please see Claiming a child as a dependent when parents are divorced, separated or live apart for more information. But it seems that this doesn't apply to you because your wife is just temporarily away to take care of her father.
Please see Who can I claim as my dependent? for additional information.
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