Abatement - division of debt between assets

I am dealing with an estate where there is no residue due to outstanding debts. The only assets are two properties - property A worth £400k (subject to a mortgage of £150k at death) and property B worth £120k (no mortgage).

Different beneficiaries receive each and so I need to apportion estate expenses and debts between the two properties.

I am leaning towards using the EQUITY in each property to work out their rateable shares - i.e., 250/370 and 120/370 respectively.

The beneficiaries of the lesser share think that it should be based on the value of the properties (notwithstanding that property A is subject to its own debt).

How would other members approach this?

Many thanks
Damian Lines TEP
Rubin Lewis O’brien