Need Advice On Going About A Divorce Please

throwaway because i want to stay anonymous

basically my parents have been married for almost 2 decades now. currently, my father lives in the uk while my mother lives in her home country in southeast asia. they have 3 daughters, 2 adults and 1 still underage. my father also owes my mother a large sum of money (the real figure is yet to be calculated) because my mother has been transferring him money regularly over the years which he promised to pay back and never did. there are some screenshots and conversations saved of this but it is incomplete as well. my mother has been wanting a divorce for nearly a year now but we have no idea how to go about it, plus my father would definitely not take it well. i am almost certain he is mentally deranged (he has been physically abusive towards myself and my sisters all our lives). there is no way to go through it amicably. plus my mother cannot leave this country to do it in the uk (where they first officiated the marriage) because of work, and divorces take really long. is there anyway to get it done overseas? or any way to have my father pay my mother back? and would there be issues over custody of my little sibling? both my parents want her but we are all against her being with my father (she currently lives with my mother). the thing is my mother has a family business that technically isnt official (its southeast asia guys) but my father has an official job at a company in the uk. does that make it complicated? the only plan we have right now is to wait for the business to settle down more and see what to do from there. waiting seems like a good option but soon we'll have to get passports done and other stuff which require his information and cooperation which he just may not give. help??