Life interest in property and professional fees

I have clients that are married for second time and don’t get on with each other’s children.

They wish to leave a life interest in the property for the survivor.

Residue is to pass to their own respective children and below £50k on each side.

They have good pensions to provide survivor with an income.

They are adamant that they want professional trustees due to the issues in the family.

My concern is how do I ensure that the trustees fees for administering the trust i.e trust registration, dealing with insurance and any other issues that might arise get paid if only half a property in the trust and no cash assets. The property is worth £600k.

Obviously this is fine if property is sold in the future and income is managed for survivor.

They seem happy that the survivor pays all outgoings whilst living in the property as standard in most precedents I have looked at but doesn’t cover professional fees.

I have suggested a life interest in whole estate for survivor to ensure some cash assets to pay fees but they want residue to go to children on first death.

How do others get around this? Does anyone have a clause that covers this.

Any help would be greatly appreciated