Can the Forster parents of the mother thats passed away try to get custody of her kids over fathe

The mother that had custody of the kids has passed away. The whole time she had custody the father of the kids and I (his fiance) has had the kids and been taking care of them and have everything they need. The Forster parents of the mother are trying to take the kids from us. Are the able to do that at all? Wouldn't the father have first rights of custody of the kids over anyone else?
Asked Oct 24, 2014

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