I don't know about John and Charlotte, but I have the following information about Sophia Schuenke (which I believe is simply a variant spelling of Schinke):

From her obituary: Sophia Graunke was born in Zachow, Stettin, Germany, on June 17, 1831, and died at her home in this city on Wednesday evening, April 28, 1909, at 8:30 o'clock, aged 77 years 10 months and 11 days. She was reared and educated in her native country and was there united in marriage with Louis Graunke on October 16, 1863. Her maiden name was Sophia Schuenke.

In 1856 she immigrated with her husband to Ontario, Canada. Here the little family, hopeful, happy and industrious, devoted their energies to farming. After eleven years' stay in Ontario, they joined a little band of Germans who foresaw better advantages in the States and immigrated to Nebraska and settled here in October 1867. This county has been their home for over forty years.

Upon coming here, her husband took a homestead in section 15, Elkhorn township, where they lived six years; sold out, rented land for three years, and then purchased 80 acres in section 34, where they remained ten years, then sold again and bought 120 acres in section 36, where they lived twelve years, then moved to West Point, their home the past eleven years.

From another, almost identical, but shorter obituary, this additional clue was given: She was converted soon after they came to America near Crediton Ontario.

The conversion was to the Evangelical church.

If you find a connection between your John and the above Sophia, please let me know.

Julie Middendorf
mjmiddendorf@nctc.net