notice of severance of joint tenancy

My solicitor is sending to the land registry for severance of the joint tenancy of the property my husband and I own - why is this and what will it achieve? My husband and I have already agreed a private settlement regarding finances and I will not be requiring any further assistance so why is this necessary?

Most married couples are "joint tenants" of the family home - it means you own it equally and when you die, ownership of the house automatically passes to the other joint owner.
If you're divorced and still "joint tenants" when you die, whoever dies first will automatically inherit the other joint tenant's half of the house and you can't override that in your will.
If you want to leave your half of the house to someone else you have to "sever the joint tenancy" and become tenants in common - you have to tell the Land Registry so they can change the house deeds to show you're tenants in common.
If you sever joint tenancy and become a tenant in common you will no longer automatically inherit the house when your ex-husband dies.

I'm thinking of severing joint tenancy until the family home is sold to protect our adult children who live in the family home with me - if I get run over tomorrow, as joint tenant their dad would own all the roof over their heads even though my will says he will get nothing I own.Joint tenancy takes precedence over a will.I want them to get my half of the house no matter what happens.

The Land Registry forms to register as tenants in common are downloadable and look straightforward - how much will a solicitor charge to do it for me?

My wife's solicitor sent me out this form over xmas but it also included a phrase along the lines of signing "all equity" over as well which I thought was strange.

I havent signed this letter yet but my wife thinks that it doesnt require a signature from me in anycase, as it is a form of serving notice rather than requiring a signature?

I am going to see a solicitor for a free consultancy and hopefully he can explain in more detail. If its simply as explained in terms of if she dies I dont automatically get the house thats fine. But until a divorce agreement is settled I'm not signing anything that affects the equity in the property over.

Does anyone know how long the separation order lasts, or is there a time limit on them?
Also is there any pre-conditions if living outside of UK? and is there any obstructions to passing on of my half of the property to my new wife and son, in case something should happen to me.
I am worried that they will be left with nothing, or have to fight for it through the courts.