Is it permissible for a new Muslim to combine and shorten prayers out of fear of their conversion to Islam being revealed to their non-Muslim family, and is it permissible for them to combine only, or to shorten and combine together?

It is impermissible to feign disbelief or utter words of disbelief, except in cases of extreme necessity. As for concealing one's Islam, it is permissible for a predominant benefit, while it remains obligatory to strive to declare it and invite others to it whenever possible. However, shortening prayers is only permissible due to travel. As for combining two prayers, it is permissible out of necessity according to many scholars, such as when one fears harm by separating the prayers.