Well now, if you had a sachet of wine yeast which was stated to be sufficient to ferment up to 5 gallons, it is usually recommended that you don't try to split that for more than two or three 1 gallon batches.
However, it seems to be accepted wisdom on other forums which deal with subjects which we aren't allowed to discuss here that you can get a cleaner tasting wash if you use less sugar than instructed (5kg max.), only half a pack of yeast, and let it take as long as it needs.
Therefore, you should certainly be able to split a pack for 5x 1 gallon.
If you're trying to push the alcohol level to the maximum then I think the 2-3 rule would apply, and you need to use brewing sugar, and then carbon filtration.