Joannine, I am going to go out on a limb here and suggest that your ggrandfather, William Wallace Crump was probably a second or third generation immigrant. Several reasons for this. First, Malvina's husband appears to have been a John Crump. Acording to the 1880 census, she was in Penn, Sullivan Co, Missouri at the time of the census. According to that John was 52 and she was 27. I cannot account for that. There is a Florence Crump, 1 yr. old living with them as well as a Mandy Crump, 58. Don't know who that could have been either.
As for the nationality, I suggest these Crump were Scottish based strictly on the name William Wallace. As you may know William Wallace was the Scott who challenged Edward I in the late 1200's. He was captured and killed. See the movie Braveheart for the story, but a hero to many Scots. Many, maybe even most Crumps in New England the New York area werre descended from Crumps from England, Ireland, and Scotland in the 19th and early 20th centuries; and many came through Canada on through the 1920's.
Of course your brother could probably prove that with a DNA test. I can provide more details if you are interested. As I said earlier, that may not prove the line, but it could. Especially if Wallace's ancestors were here earlier than I think they might have been.
Wallace sure got around. We find him in Wyoming, New Mexico, his family in Louisiana, Texas, and Missouri that we know of. Maybe other plsces. He was listed as a mechanic in a garage in the 1930 Wyoming census.
If you know where he died you can probably get a death certficate since he died more than 50 years ago. I have found that is sometimes a good source, but it depends on who gave the information.
You mention that Malvina might have been born in Louisiana. It's possibe, but according to the records she was born in 1833. That's consistant with the birth of Wallace. I know all but two or three of the Crumps in the Census of Louisiana between 1850 and 1880 and do not find that name. Neither do I find any Wallace nor any William other than the ones I know.
My father-in-law was born in Blossom, TX. It was an oil well town and maybe Wallace worked in the oil fields? That may be consistant with NM and WY.
Let me know what you think about all ths. I cannot seem to get into the message pages at Ancestry.com, so will have to restrict myself to this forum unless you want to give me your email address and we can talk directly. Mine is firstname.lastname@example.org, but I may answer from another address.