I don't know where you live, but if it is in TX, many of the public libraries have the TX state wide death index 1903-1940 on microfilm.If not, contact the State Archives in Austin, they have it and will look for death of Lois Mann.They can give you county and date of death.Then you can obtain a copy of her death certificate, which "should" show the names of her parents.Accuracy of DC only as good as the knowledge of the informant.
The 1900 census shows Lois had 6 children, with 4 living at the time of that census.Maybe daughters whohave married and left home(?)If you can find an obituary for Lois, survivors are usually listed and it is also a good way to pick up married names of female members of the family.
Once you have death date for Lois, check with the public library in Perrin, see if they have microfilmed copies of old local newspapers, if they don't, they should be able to tell you where you can find them.
Check probate and land records, when final sale of land is made heirs will have to sign off to give clear title to buyer.The 1900 census shows Joseph owns farm free and clear.There are more records out there then Bible, census and gravestones, some we just don't think about.