Considering the various comments above, it is a bit of a guess as to what exactly you want to say, but given your clarification, I think enough context was given to provide you with an answer.
For future reference however, please check the Help Center of the Stack Exchange site you are visiting to ensure that your question is within scope for the given site. This will ensure that your question is answered sooner, and by people who are good at answering your particular kind of question.
That said, the problem with your sentence is that the different parts of your sentence mean different things to the extent that putting them together doesn't make much sense:
- As of when (Since when, referring to a past event)
- the man and woman take him in (sentence suddenly in present tense)
- his reaction in the face of danger is to curl into a fetal position. (present tense as well)
When you want to express the change in how 'he' reacts to danger from the moment he was taken in by the man and woman (so not before he was taken in), all parts of that sentence have to match up, not just the 'as of when' part, for example:
Ever since the man and woman took him in, his reaction to danger is to curl up into a fetal position.
Keep in mind that this only says something about how the person responds after having been taken in, not how he responded before (only that it wasn't by curling up), but for all intents and purposes, this should give you some insight into how the sentence is built up and how you can expand on it yourself.
To parrot myself however, do consider asking questions about correct grammatical tense, etc, on the Stack Exchange that better suits your needs, the English Language Learner site.