Adding trustees to house deed

My husband will created an immediate post death interest, leaving me a life interest and his 50% share in a trust for his two children. My question is I cannot sell the house as tenants in common on my own. How do I add my children name as trustees to the title deed. I have asked my solicitor and he said probate is needed. If I understand correctly as a sole survivor I can transfer the whole property into my name and my children without probate.How do I go about it and what forms do I need?  Also do I have an option to add them as trustees or legal owners as a I understand as trustees they are not legal,owners. If I add their names as trustees will it be registered on the title deed? Not sure whether my question is clear. Thanks

Jan - it's a common Q to ask and whilst we can direct you to the forms needed to do X or Y it's legal advice you need as to which option is the right one for you and your children
You are correct that you don't need probate as the legal ownership of the property does not form part of his estate. It can though still be used as evidence of his demise.
I should also add that you can still sell the house but you have to account for his beneficial interest/the TIC aspect when doing so. One option is to appoint someone to act with you and together you then sell/transfer to the buyer. 
If you decide that you do want to transfer the title to yourself and your adult children then our online assisted guidance will help re the forms and procedure - HMLR Guide: Start - External  · HM Land Registry
If you decide that you want to set up a trust with the children as trustees then our PG 24 offers guidance from a registration perspective - Private trusts of land (PG24) - GOV.UK
But please do seek appropriate legal/financial advice to understand what options you have, the impact on you/your children going forward and more 

One option is to appoint someone to act with you and together you then sell/transfer to the buyer
Pl how do I do that? Is that the same as adding a trustee? My children are trustees of his 50%? Is it a conveyancer I need to see?  As probate solicitor insist I need probate! 

Jan - it's a conveyancer or conveyancing solicitor you need to seek advice from
You need guidance on the difference between beneficiaries and trustees and how the 'trust' you both created now impacts following your husband's death
See PG 21 section 6 for guidance on how a sole owner can transfer the property where a form A restriction is registered
Practice guide 21: using our forms for complex and more unusual transactions - GOV.UK