I have altered challah recipes to accommodate smaller amounts if only making 2 challahs, or want to use a breadmaker. The average 5 lb bag of flour contains about 18-20 cups of flour. You can measure exactly if you want, Don’t dip the measuring cup into the flour bag directly, but scoop out the flour with a large spoon and gently fill the measuring cup each time, so the flour is not too compacted in the cup. If I want to use only 5 cups of flour, you must reduce everything by the same fraction. So if your bag holds 20 cups of flour, and you want to use only 5 cups, that’s 5/20 or .25. You must reduce the other ingredients by .25 or about one quarter. Dividing the other ingredients by 4, gives you 75ml or 5 tbsp. of both oil and sugar/honey combo, 1.25 cup of water, etc, just divide by 4. Use 2 eggs, This will now fit in the breadmaker. As the recipe says, if the dough is too wet, add small amounts of flour as needed, Open the lid of the breadmaker and check how wet it is, I often find I must add small amounts of flour, even with a breadmaker, depending on the weather.
The same recipe can be made by hand, kneading the dough till soft and pliable. This will make 2 medium challahs.
Regarding fresh yeast:you need to use twice as much fresh yeast as dry. So 1 tbsp of dry yeast is equivalent to 2 of fresh.