Mutual Divorce

I am (38M) married to my wife (39M) since last 6 years. We have usual marital issues between us which are unable to sort. We have given it a try but could not work it out. Due to frequent fights & ongoing issue, we have not been intimate since last 3 years. We don’t have kids. We co-own the flat we are staying in. Both of us pay EMIs of flat. I pay 55% & she pays 45%. Downpayment of flat & registration expense was done by me. Now we have decided go for a mutual divorce. They are demanding the flat in place of alimony/maintenance. I have paid close to 40 lacs for the flat (Downpayment + EMI). If do not accept their demand, they have threatened me to go to court. My wife is a working woman since last 13 years & earns well while my earning is 2 times her earning. I have offered her to pay the amount which she has spent for the flat (EMI+interior) & the interest on that amount. But they have declined this offer & they are adamant on their demand. I need advice from the learned legal professionals if her demand is valid & if it goes to court what chances do I have to retain this flat?