If I have a [Sanji] with 6000 base power or less on my field, does this card in my hand get −5 cost?
No, it does not. This effect allows you to give this card in your hand −5 cost if you have either a "[San-Gorou] with 7000 base power or more" or a "[Sanji] with 7000 base power or more" in your Character area.
If I have both a [San-Gorou] with 7000 base power or more and a [Sanji] with 7000 base power or more on my field, can I give this card in my hand −10 cost?
No, you cannot. This effect allows you to give this card in your hand −5 cost if you have either a "[San-Gorou] with 7000 base power or more" or a "[Sanji] with 7000 base power or more" in your Character area.