iPhone on silent except for calls
Put the contacts you want to allow to call you when you are sleeping to a group an give that group a name.
Then: Settings > Do not Disturb > Allow Calls From > select group of contacts that you created.

Additionally you may select to allow repeated calls (if someone will call you second time within 3 minutes - you will hear it) and choose Scheduled if you want to schedule your Do Not Disturb to switch on automatically.