When dealing in noun clauses, such as your first example, it is when the verb itself is doubtful (préférer que, regretter que) that subjunctive comes in to play. It can also go with the negative forms of croire and penser, but not the affirmatives. Savior, to know, is a definite verb, so I don't believe subjunctive would be used here.
In adjective clauses, such as the second example, one uses the subjunctive if the whole of the antecedant phrase is negative or indefinite. As "I don't know if they..." is a negative phrase, I believe you would use the subjuctive in the second case. Were it changed to "I know they are not with us" then it would be back to the indicative, as "I know they..." is an affirmative statement, even if it becomes negative later on.
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Dans mon lit je rêve à Lilly Town
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