The simple answer is yes and no, but you can only use assets you downloaded from the marketplace for commercial use. If your friend did buy any assets, you cannot use them if you don’t pay for them , or downloded the assets from the marketplace. So the answer is: If you did download the assets from your account from the marketplace, then you can use the for your game and earn money, unless Epic Games send you an e-mail and and tell you that 1 or more assets cannot be used. For non commercial use, like you help someone or make a game, then you can use them as long as you don’t give out the game.
This links will give you the info you need:
https://marketplacehelp.epicgames.com/s/global-search/license?language=en_US