using sim and apple id on sisters iphone

Well, it would essentially transfer ownership of your sister’s iPhone to you, and leave your sister without a phone. Is that acceptable to your sister? To do this your sister would have to follow this guidance→What to do before selling or giving away your iPhone, iPad, or iPod touch

Also, if your sister has a US iPhone 14 it doesn’t have a SIM slot, so you can’t put a SIM card into it.

Possibly.

• The photos she has on her phone may be added to your iCloud and she may get your iCloud photos on her phone.
• The same is true for the Contacts.
• There is always the chance of data loss if your sister does not have another device using iCloud, as her iCloud data will be removed if no device is connected to it for 30 days.
• If she has any payment methods added to the Wallet, they will be removed when she signs out.