first of all, you can all give tzedakah to causes that you think are important.
but, it is possible for someone to have bitchon and not expect to take money from parents and in-laws. i know people where wife works a little (not to make herself ragged; husband learns and tutors or other little jobs and they have bitachon for rest. and Hashem does give them money without them going begging. (ex. $150,000 yerusha – the couple nevern knew person was rich or expected that money). and Hashem has many means to help, and nobody should help if not important to them. i too would give first to starving, sick, etc. families.
amt. of hishtadlus is dependent on many factors – no clear cut answer for all.