EU unmarried partner application - should we send a second passport?

[Triplelgirl]

Hi, am an eu national and my partner is dominican. He is going to apply for residence card as my unmarried partner.
He was brought here by his momy who is also a ea national she attempted 3 applications but home office refused as there wasn't enough evidence that he was living or was dependent of her. We been together since 2015 and been living in the same property for more than 2 years and have a 8 months old baby.
He applied for a a new passport because he thought the other was lost but someone told us that home office has it. That they don't return it when they refuse a permit. Our question now is should we send the new passport with this new application or shall we not ? Someone told us not to send it but we are very confused. Please help