There is no threshold with foreign bank interest when considering if you meet the criteria to complete a Self Assessment form.
If you receive any interest from savings outwith the UK you are required to sumbit a Tax Return.
You will still qualify for the £1000 Personal Savings Allowance against this income.
You would need to register for Self Assessment and also declare your worldwide income.
Register for Self Assessment
The £500 received as a gift from family is non taxable.