Can files be exchanged between FAT32 and HFS+ partitioned drive?
It might make sense to make the entire drive FAT32 to ensure readability between systems, unless there is a need for having multiple partitions not described in your question. As for the specific answers,


Yes, dependent on #2
The files MUST be moved on a Mac because a PC cannot read an HFS+ partition by default and even then, cannot read without special software. Your friends would only be able to read the FAT32 portion of the drive.
Yes, your older Macbooks should be able to read the partition, and compatibility exists all the way back to OS 8.1 (source)