In The Metamorphosis, how did the family survive financially when Gregor turned into an insect?

In the second chapter,
Gregor learns that "in spite of all their misfortunes a bit of capital, a very little bit,
certainly was still intact from the old days, which in the meantime had increased a little
through the untouched interest." In other words, there was some money left over after his
father's business failure, the failure that meant Gregor would have to work in order to pay off
his father's debt. One might imagine that this money would be put toward Mr. Samsa's debt, but
it was not.

Further, Gregor learns that the money he's been earning each
month "had never been completely used up and had accumulated into a tidy principal."
This is, of course, a surprise to Gregor because he assumed all of that money, except for the
very few dollars he kept for himself, had been used to pay down the debt. Had it been used in
this way, he would have been free of his horrible job sooner, but now, at least, he is glad that
his father exercised such "forethought." It likely seems to the reader,...