Unable to set base folder for external sdcard

[catsmeow]

I have a Samsung Galaxy Tab 7.0 Plus (GT-P6210). It has both internal storage and a SD card. Families is using the internal storage, but I want to use the SD card. I've attempted to change the base folder but Families Settings tells me the folder "cannot be accessed" and won't accept my entry.

I had created a families folder on the card, and had successfully used Families Sync to manually put my main Legacy file onto the card, but in hopes of getting Families Settings to accept the path, I formatted the card. Families Settings still won't accept the path. The path I'm trying to enter, based on "My Files" which came installed on the tablet is:
/mnt/sdcard/extStorages/SdCard

I can transfer the file wirelessly into the internal storage, but I'd prefer to use the SD Card rather than use up the limited memory.

FYI, I'm pretty computer literate, but not at all tablet literate. This device is fairly new, so I'm still struggling to learn how to use it. Thanks for any suggestions!
Helen