Q: Re entry permit

My parents has a green card. My Grandma got sick and my parents applied for the 2 year re-entry permit "White Passport" and wend to help. The Two year expired January 2019 and my Grandma needs till June to improve so my parents can come back to the USA. If they come back, will be denied entry ? What do they need to do. Should they get doctors medical report with them. Thanks allot

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