Possibly the best advice for avoiding over-dependence on sources and others' interpretations, is to develop your own 'voice' as a writer.

It is absolutely essential as a PhD researcher, you contribute something original to the field in which you are working. It is largely through your writing that your achievements, and the extent of originality in your contribution, will be communicated to your peers. It is vital then, that your readers are able to distinguish between your own work, and that of your sources.

An important way of developing originality, is through writing. Rather than 'learning to write', think about 'writing to learn': use writing as means of developing conceptually. This is an important way of discovering your voice as an academic writer in your own right.