Consecutive infinitives
There is no grammatical limit. The sentence could continue The witness refuses to consider to agree to testify to help to free . . . However, anyone writing like that would quickly try the patience of the reader.
No. This is a style choice. Once you get past two infinitives, however, you might start considering revisions, simply for the sake of flow and ease of reading.
E.g.: 3 infinitives: The witness refuses to consider to agree to testify. 2: The witness refuses to consider agreeing to testify. 1: The witness won't consider agreeing to testify.