Office of Grand Ayatollah Sistani (may Allah grant him long life):

If Taqiyah (dissimulation) requires you to fold your hands, you can fold them during prayers.

Office of Grand Ayatollah Makarem Shirazi (may Allah grant him long life):

If a person folds his hands (as done by the followers of some Islamic sects) or puts them on his chest as a mark of humility and reverence, the precaution is that he should repeat the prayers, even if it does not look like them. However, there is no harm if it is done forgetfully or due to helplessness, or for some other purposes, like, scratching.

Office of Grand Ayatollah Saafi Gulpaigani (may Allah grant him long life):

If it is possible to delay your prayers so as to offer your Salat in your home without folding your hands, you should delay it; otherwise, you can fold your hands and offer your prayers under Taqiyah.

Ayatollah Mahdi Hadavi Tehrani's answer to the above question is as under:

It is permissible to exercise Taqiyah wherever the conditions of Taqiyah are met, be it reconciliatory or out of fear. In some circumstances, exercising Taqiyah becomes obligatory.

Given that you are afraid lest they should harm you, it is permissible for you to do Taqiyah and fold your hands during prayer. Of course, you should note that folding hands in prayers has neither been considered as a recommended act nor as an obligatory one.