荷物を親から送ってもらうが、来週中に届くから来たら教えてって英語でなんて言うの？

In English it is a common error to give too much information when youi ask for something. In the first reply, "I'm expecting a package (from my parents) this coming week. Could you let me know when it gets here?" you have included a lot of information. You could ask yourself, "Is all that information essential?" Firrstly, who you receive parcels from is your business and only yours. It is not necessary to state where, or from whom the parcel is coming. Compare that with the second sentence: "Please let me know if a parcel arrives." Of course, just to be friendly, you may choose to give more details, but it is really your own private business. In the UK, people who always give too much detail in their speech are often considered to be A, stupid, or B, have no conception of personal privacy.

"My parents are sending me a package/parcel it is supposed to arrive sometime next week. Can you let me know when it arrives?" "package" and "parcel" both have the same meaning. This explains to the family that your parents are sending you something and it is meant to arrive in a weeks time, It also asks them to tell you when it gets there. "There should be a package arrive for me next week from my parents, Can you please tell me when it arrives?" This explains to them that your parents have sent you something and that it will arrive next week, and can they please tell you when it gets there.

If your parents are sending you a parcel then you could simply say 'Can you let me know when the parcel arrives from my parents please' By adding please is a polite way of saying it. You could also use the term 'package' as well as 'parcel' to mean the same thing.

"My parents will be sending me a package, would you please let me know when it arrives?" by asking for them to let you know when it arrives, they will know to notify if it comes and then they will also be expecting it to arrive.

When you want to ask your host family to let you know when a package from your parents arrives, then you may ask in the following ways: -My parents sent me a package and it's due to arrive in a week or so. Could you please let me know when it arrives? -I'm expecting a package from my parent in a week or so. Please let me know when it arrives

This is minimal information and all you need to say. However, as you are staying with a host family it may be polite to include more information, that it is from your family in Japan and that you expect it next week. 'My parents in Japan have sent me a parcel. It should be delivered next week' 'I'm expecting a parcel from my family in Japan next week' Parcel = package Delivered = Brought to the specified address

In this case, you are having something sent to another person's house and therefore they are doing you a favour so be very polite and use the could/would form. For example, "I hope you don't mind but my parents have sent me a package from Japan and it should be arriving next week. Would you let me know when it has arrived?"