With our daughter constantly leaving us with her children whom we have custody of, can we adopt?

My wife and I have two beautiful grandchildren who we have custody of through DSS. My daughter has repeated left us with no contact for days and a week at a time. WE tried to be supported of her, but she keeps abusing us this way among others. Our thought was to first befome foster parents to help defray the cost of taking care of our kids, and secondly adopt. We have had all the psycological testing from DSS, home evals, etc. What are thoughts on this?