There are a number of resources about the Gilbreths on the web, but many are outdated and the rest tend to be brief.
There are, for example, a number of short biographies of Frank, Lillian or the couple, mostly on university and organization sites. Nearly all of these repeat the same basic information. A number of the institutional pages move around their larger framework from time to time as well.
A currently validated list of sites includes:
These two sites were created and maintained by David Ferguson for a number of years, but ceased being actively updated well over a decade ago. The free host that holds both sites (Tripod.com) appears to be safe, but in these late, unattended days the first site generates endless popup windows and ads in the manner of sites known for malware. Use caution, but they are worth at least one visit before they disappear.
The significant material from both sites has been added to the archives here.
“The Wiki” of course contains several entries related to the Gilbreth family and their interests. None is especially enlightening but all contain some material of interest. The link leads to a group entry; other searches may be of interest as well.
An occasional search using selective terms will return newer and unusual material, but honest... it's been a long time since anyone added new or expanded content. If it's not on this site, it's very deep in old publications or in management science papers and articles. Do let me know if you find something significant that's worth including in this list!