Does your friend not have Lazarus' and Rachel's marriage certificate?
Lazarus Blumberg m. Rachel Pizar
Q3 London City vol 1c p288
The 1891 census reported that Lazarus came from Riga (where some of your Fellmans ended up). Riga was the captial of Courland/Kurland. Although formerly a province of the Russian Empire, Courland was ruled by Baltic German nobility until the 1880s. There was a very strong German cultural and linguistic influence. It is no surprise that Lazarus identified himself as German.
The surname Pizar/Pizer is derived from Peizer (ei is a long vowel sound, like ie in pie), the German name for what is now Pyzdry, SE of Poznan. Peizer was on the Russian side of the border between the Prussian province of Posen and Russian-ruled Congress Poland until 1918.
Justin