You must add the child support to the fafsa , did you add the child support received to the FAFSA?
If your grandparents are willing to do this, why don’t they just pay it to the school? I can understand your mom not having the most stable financial situation, not taking out PLUS loans of 40k+.
To add on to what Thumper said, Syracuse does not meet 100% demonstrated need. The closest they come to meeting 100% are NYS students who are admitted through HEOP and then they were given a lot of loans.
My experience dealing with Syracuse for a student with a 0 EFC was she had a really big gap in her financial aid package (this was after her non-custodial waiver was approved). We made a lot of phone calls to to the regional admissions rep who I knew, who recommended us to another program for economically disadvantaged NYS students. The person in charge of that program, happened to be attending a program in NYC and we set up a meeting in NYC for my student to meet him, to get some extra funding.