I haven't found the Madsen brothers in Wilton, Muscatine County, Iowa so more hunting needed.
Here's the family in Denmark. At least this gives the full name including middle name and birth years of the brothers, which will help in locating them:
1880 Sønder Draaby Flade Sogn (Parish), Sønder Draaby, Morsø Nørre, Thisted, Denmark Villads Madsen 39 married, all people in family born in Draaby parish, Thisted amt Ane Nielsen 37 Mikkel Knudsen Madsen 8[born about 1872] Peder Kristian Madsen 6[born about 1874] Niels Kristen Madsen 1[born about 1879]
This place in Denmark is situated on the island of Mors, in the Limfjord of northwest Jutland. [Sønder = South]
1892 Immigration (entering USA) found by Danish genealogist poster: Arrive New York 05 March 1892 on the ship Hekla Mikkel K. Madsen age 20 [born about 1872] Peter K. Madsen age 18 [born about 1874] Destination Wilton, Iowa