I would say they could bring the stuff over, but they shouldn't expect the stuff back in the future since you will get rid of any baby stuff you don't need. If they are willing to give it to you on that basis, I don't see the downside. If her stuff is truly the same as what you've been given, then you could return the new stuff and exchange it for a credit. I know in the first few months, I made several trips to the store for baby socks and Tommy Tippy bottles. If your new stuff is better, then consign the IL's stuff. If the consignment place won't take something, then freecycle it or put it on Craig's List.