Lots of good advice and preps in previous posts, to which I would add, remember that illness or injury, or lack of time may prevent doing the laundry by hand.
Therefore also consider keeping at home a stock of old underwear, sheets, outer clothes etc.
In normal times launder and store old, just about useable, cloths and linens. Then when any emergency occurs, these articles can be used and tossed out, its no waste if they were due to be tossed out anyway.

Hand laundry for a large family would be a bit of a challenge, if power failures are the main problem then consider either larger stocks of cloths and linens in order to postponne laundry day until power returns, or a generator able to work a washing machine. (presuming that you have enough water)