My wife is doing the online business for her mother’s brick and mortar business. Unfortunately having the brick and mortar store doesn’t help all that much for the inventory situation. That’s because you can sell 1000 different SKUs with only 1 of each in inventory in a brick and mortar store. But online you better have only 1 SKU and 1000 of that in the inventory. It takes effort to put a SKU online as you need a description, picture etc. for each.

You might want to keep that in mind when looking at helping your wife & sister to bring their business online. For example by having a reduced availability or offering a live video call service walking around the store and let customers choose that way.