Complex sentence: Henderson lived with Davidson and his wife, and he initially worked for Davidson as an unpaid associate, but several large commissions in late 1868 helped catapult the venture into financial success which enabled Davidson to send money home to his family in Scotland.
Split into simpler sentences: Henderson lived with Davidson and his wife, and he initially worked for Davidson as an unpaid associate. Several large commissions in late 1868 helped catapult the venture into financial success which enabled Davidson to send money home to his family in Scotland.