Grandparents paying tuition - children at CSS schools

My parents offered to help with one semester of tuition for each child. Child #1 is entering senior year and Child #2 is going to be a sophomore. Both receive financial aid at CSS schools. Now that we have completed all of #1’s final financial aid paperwork, we planned on having the grandparents pay Child #1’s tuition directly to the school this year. (I know we have to wait for them to pay Child #2’s tuition until later on in sophomore year).

Is there any downside to doing this in terms of child #2’s expected aid for next year?

Would it be better to wait and have them pay the spring semester bill after we have filed Child #2’s FAFSA & CSS for 2018-19 (instead of fall this year)?

If the payments are made directly to the school or to the student (child #1), I don’t think there will be any downside to child #2’s expected aid.