Can i marry again without permission of 1st wife

I had married to muslim girl her age was 23 after marrige twice she had miscarriage which was done intentionally by my in laws 3rd time we had taken care and girl was born who is now 1 yr old later on my wife was facing dizziness etc so we went to doctor where we come to know that my wife has pulmonary hypertension with ASD means 2 holes in her heart which from her childhood doctor said that there is no gaurantee of her life she might servive for few years but doctor has not mentioned exact figure when we ask this to in laws they said we hide the truth you remarry in our relatives but this kind of deases is their jeans few past deaths with same health conditions still we did all our tries for her treatment now there is no other option remain my in laws got chated in some funds and they are now bankcorrupt now my wife is demanding 10 laks or flat to me for permission of 2nd marrige i said if its for security i will give you what you want but you can not sell it it will go to my child.