Who should be responsible for taking care of elderly parents- Both daughters living abroad

Parents were settled in Delhi from 1971-2010 &both daughters got married from Delhi. The elder daughter(current age 48),along with husband(current age 53) & son(current age 21) moved abroad in 2010,due to husband's work assignment.While moving abroad in 2010,they did not give any clear answer to whether they would be returning back as everything was dependent on the job. But said that they would work out something for parents who they were leaving behind in Delhi(Current age mother 77 & father 80) but never gave any concrete plans. Younger daughter (does not have any child,medical problem) -Current age 42,moved to Mumbai after marriage in the year 2005 and then moved abroad in the year 2014 with her husband due to husband's work assignment. Parents - Relocated to Kolkata in 2010 as they were depending on the elder daughter who had been staying in Delhi as them.Parents took the decision to move to Kolkata as they were not comfortable living alone in Delhi upon elder daughter moving abroad. Younger daughter in Mumbai that time had undergone surgery and had some marital discord.Parents also they had some personal financial constraints.Considering all the aspects,they decided to move to Kolkata to be around relatives. Parents supported the elder daughter's decision when relatives asked about the sudden relocation and told everyone that they cant move with younger daughter in Mumbai due to factors like marital discord. Younger daughter helped with relocation, took care of parents single-handedly during [deleted] with the little help of relatives.Mother had suffered health issues.Had traveled frequently to Kolkata. Meanwhile,the elder daughter kept sending money as she was away and to keep a hold on parent's assets and kept telling parents to take minimum help from the younger sister to avoid parents getting involved in her marital discord . But indirectly kept telling the younger sister to take care of parents Year 2014 to the current date: The elder daughter did 1 emergency trip from abroad when father was hospitalized but has minimized trips to parents giving son's education as a reason. The younger daughter did 2 emergency trips when mother was hospitalized,Plus keeps visiting every 6-9 months and stays for 3 months. Questions:What is the best solution to handle the situation? Everyone is pushing the younger daughter to take care of parents as she does not have a child to take care.But at the same time,no one including the parents and elder sister are concerned about how this arrangement would impact younger daughter's life since her husband would be away abroad,being childless and son in law and father in law never had a great relationship from start but he never stops her from helping her parents. Younger daughter suggested taking terns but neither parents or sister are supporting this.Younger daughter can help financially as well but parents want her to take care of them physically. Please advise. .