"Must" and "have to" have the same meaning, for example: "You must eat your cabbage" and "You have to eat your cabbage" mean the same - you are required to eat your cabbage. "Mustn't" and "don't have to" are not quite the same. "You mustn't eat your cabbage" means you are required not to eat it, you are forbidden to eat it. "You don't have to eat your cabbage" means you're not required to eat it, but you're not forbidden from eating it either - you can choose to eat it or not. There is a negative form of "have to" that would mean the same as "mustn't" - we could say "have not to", as in "You have not to eat your cabbage", but this construction feels unnatural to native speakers and so would not commonly be used.

2 is closer, but still not quite right. The correct sentence would be "Could you please send Daniel's locks to our office". When using the subjunctive "could you", English uses the infinitive format of the verb (send), not the past participle (sent). You don't need to use the definite article "the" for "locks", because you are already stating that they are Daniel's locks.

Unless there's food in the context, "to relish" usually means "to enjoy greatly". The "blood of biblical quotation" is metaphorical; it refers to how many Bible stories (particularly in the Old Testament) are very violent, or "bloody". So when it says Billy Graham "relishes in the blood of biblical quotation", it means he is reading out violent biblical passages, and clearly enjoying how bloody they are.