QuiltingCotton ... the only way to get the "right" answer would be to ASK the infusion centre, directly.
Not only about how many they will accept at a time, you should ask them as to any specifics re size, shape, fabric, etc.
There would be nothing worse than to make some quilts and to be told, they don't meet the requirements. Or worse, that they do not accept donations.
Good Luck!