Beneficial joint tenants who need a declaration of trust?

We are dealing with a transfer of equity, acting for the lady who has a new partner who will join with her on the mortgage to pay out the lady’s old partner.
Put simply, they want to own as beneficial joint tenants ie with ius accrescendi but secure to (her?and) her estate £180,000 as a first charge on the proceeds of sale net of the new mortgage.

There’s probably an easy answer that I have missed and will be grateful if the forum would tell me what I should be saying. Subject to that:

Which is better?
(1) a second charge (if the mortgagee will consent to it, which they ought to, the LTV being very low), securing to her and her estate the first £180,000?
(2) A declaration of trust by them (adding a protector who is not a trustee) to the effect that they are to be treated as beneficial joint tenants save for the first £180,000 after the repayment of the lender, title with a special restriction requiring protector’s consent/(or if no protector, prior written consent of her PR’s) to any dealing with the property by the survivor?

They don’t trust Wills, even mutual Wills, to preserve her right to £180,000.

Is there another way that we have missed?

David Martin
Kidd Rapinet