Thanks for your reply, and I am clear on matters now.
Ideally, your Father's Will should have stipulated that the Estate be responsible for arranging the Buildings Insurance and that these costs would be reimbursed by the Life Tenant.
As it stands, the Will makes the Tenant responsible for insuring. From a legal point of view, there is nothing stopping a Tenant of any type arranging the Buildings Insurance and legally you ar eunable to insist that this arrangement changes if the Tenant does not wish to change how things operate over the Insurance.
From a practical point of view, you and your fellow Executors will want to make sure that the property remains insured. I would therefore suggest that you speak to the tenant and see if she would be happy for any future Building Insurance policies be taken out in the name of the Executors. I am sure that as long as any such policy is no more than what she is currently paying, she will have no objection. Upon payment of the Policy, you would then need to get her to reimburse you the cost.
Alternatively, and this could apply to her existing policy, you can ask that the Policy remains in her name but that you and the fellow Executors are noted "as interested parties" on the Policy. This would mean that you would get notified of the Policy expiring/of any claims that are made.
I hope this assists and sets out the legal position.
As the Will is drafted as it is, this is the only "agreement" that needs to be followed, and thus the Tenant could legally object to your request, but hopefullly she will agree!