I have the issue that if anything happened to me my children may be separated. DDs SD would fight DF in court (though hopefully he would have no hope as he has only seen them once and DF has raised them from birth) and DS could be taken by his SD (as listed on his birth cert.). Only child DF would be guaranteed would be this baby as Juno is biologically his.
Ignoring all that, I wouldnt want my mother (or father) to get them, my siblings are too young (nearest sibling is just 16) and sadly my grandparents are almost 80 (they would be my ideal home for the kids as they respect our decisions and implement our way of parenting with our children without argument. The kids also love them something fierce).
DFs parents are just getting to know them and seem very overwhelmed just visiting them, both DFs sisters would not be an ideal home in my eyes (one of his sisters is married with a son but is a very different parent to us and the other sister is 23, single and constantly changing her life plans on a whim, very unstable home environment etc) and DFs brother is newly wed with a 3 month old baby but of our close family, to me, they would be the best choice.