Khums is wajib on you and your family
You may get help of local scholar to educate them. For now you fix the date, check your cash in account or at home or bank and unused stuff and unused gifts, calculate the value and pay 20% of whole. Half is sahme imam which goes to your marja or his representative or the institution which has permission to collect the khums and half is Sahme sadaat for poor and practicing syed
For past khums check and calculate and pay or get help from local scholar.