Thank you for sharing what is weighing on your heart and for trusting God even while you feel stuck between two people you love dearly. I am praying for you, for your mother and for your husband.
I am praying first for your mother and her leg. The swelling and pain that has not responded to many doctors is not hidden from the Lord. In Scripture God even made provision for those with conditions that had no human cure, showing that He leaves room for His own work in incurable cases. When Jesus came He showed that same heart. He touched Peter's mother in law when she was sick with a fever and the fever left her at His touch. He healed the leper, the servant of the centurion, and many others who were brought to Him in the evening, because all power over sickness and infirmity belongs to Him. He still has that power today. I am asking the Lord to lay His hand upon your mother, to ease the pain, to reduce the swelling, and to bring healing according to His mercy. Pray with faith that Jesus is able, and ask Him to guide the doctors to wisdom as well.
I am also praying for peace in your home between your mother and your husband. Scripture gives a beautiful picture of devotion between a daughter in law and her mother in law in the story of Ruth. Ruth chose to stay with Naomi, to honor her and care for her, and that loyalty was noticed and blessed by the Lord. That kind of gentle, faithful love between generations is precious to God. At the same time the Bible teaches that the deepest bond we have is in the family of God, and when a family is united in love for the Lord that unity brings great strength. When it is not united, it can bring deep strain, and the Lord calls us to pursue peace.
For your husband, I am praying that God will soften his attitude and give him patience and kindness in his words, especially toward an older woman who deserves honor. Love is to be patient and not easily provoked, and to bear with one another. I am praying that where he is quick to take offense he will learn to overlook a matter, to be slow to speak and slow to anger, and to let love cover what can be covered. You mentioned that he often brings up past issues and that there is darkness he dwells on. Only Jesus can cleanse the heart and release a person from the weight of the past. I am praying that your husband will bring those memories to the cross, receive forgiveness and give forgiveness, and walk in newness of life by the Spirit rather than remaining bound to old grievances. God has called us to peace, and Scripture says that a believing wife can have a quiet influence as her husband sees the life of Christ lived out daily in her.
Continue to love both of them faithfully, to honor your mother and to respect your husband, and to entrust what you cannot fix to the Lord. He sees you in the middle and He is able to keep you.
Let us pray. Father, in the name of Jesus I bring this mother before You. You see her pain and swelling and the many attempts for help. Touch her body, relieve her suffering, and bring healing as only You can. Give wisdom to those caring for her. I bring this husband before You as well. Work in his heart, cleanse away what is dark, help him to let go of past hurts, and fill him with Your peace and gentleness toward his wife and her mother. Give this daughter and wife grace, strength and wisdom to walk in love, to speak with grace, and to rest in Your care when she feels stuck. Let Your peace rule in this home. Amen.