Child Guardianship

Hi
when I was in my early twenties I gave up custody of my two children to my grandparents who had raised me....upon finally maturing they had become so close to my Grandparents and were doing well knowing it would tear my Grandparents apart I did not seek custody but saw my children as often as I could....

I have another daughter that I have had custody of all of her life...and have a wonderful husband now that is her daddy (step)
my grandfather passed away in January and because of my grandmothers failing health and inability to care for the children any longer they were sent to live with my husband and I....I now am faced with only a piece of paper signing over guardianship with a notarized signature of my grandmother....and need to know if this is legal or not and also whether their social security will continue for their support or not and what should be done legally to seal anything.....my grandmother has sworn on one day to give up custody to us and then the next she says she will not til the day she dies**************she lives in KS and we live in TX...what is our next step?