My sister is passing away in a hospital in Iowa after complications of surgery 2 weeks ago

My sister is passing away in a hospital in Iowa after complications of surgery 2 weeks ago. She had no will, trust, etc. She has 3 kids from 3 different fathers, the most recent being 5 months old. She is not in a relationship with him, but they have lived together with their kids for about 2 years. Before her surgery she sent me a text asking me to take custody and raise her children if anything were to happen. She has had 2 heart surgeries in the past, this was supposed to be the final with her mechanical valve. 

I believe I will have issues with the father of her current child. He has no job, they don't own their home, and can't care for their baby. What do I need to do now and in the next coming weeks, to hopefully get custody of her children and their care and keep them together?

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NAL- UIHC? Ask for a social worker. If you sister is of sound mental mind, a will can still be established and they can help you with that. The issue that will come into play is a believe the fathers will have the first right regardless of her will.