1-What is the difference between 'backlog' and 'loads of work'?-- 'Backlog' is work that should have been completed before. There may be a little of it or loads of it.
2-What is the difference between 'concidence' and 'by accident'?-- 'Coincidence' suggests luck.
3-Is this sentence correct, 'He derives his power from his family'?-- Yes.