"...how can adult children guard against the surviving parent selling property and not divvying up proceeds?"
There will be a statement on the Land Registry form for the property that reads something like this:
"No disposition by a sole proprietor of the registered estate (except a trust
corporation) under which capital money arises is to be registered unless authorised by an order of the court"
This stops the surviving spouse from selling the property by themselves.
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"...no problems with adult children needing /wanting the house atm"
However, if the house is sold then the trust's share of the money cannot be divvied up among the children until the surviving parent passes away.
The trustees can choose to use the money towards helping the surviving parent buy a new home and the trust will then own 50% (or whatever share it is) of that new home under the same terms.
If the trustees choose not to do that then they must invest the money until the surviving parent dies. The surviving parent gets the income but cannot touch the capital Only after the death of the surviving parent can the children get their hands on the money.
If that happens then I would strongly suggest speaking to a qualified advisor.
Any capital growth is retained by the Trust, but any income (such as interest or dividends) is paid to the surviving parent.
For example, if you put £100k in a savings account. According to Moneysavingexpert, the top rates at the moment are around 4.5%. So £100k in a savings account could earn £4,500 per year in interest and that must all be paid to the surviving spouse.
That's great for them but not so great for the children.
Alternatively you could invest in things that go for capital growth and don't provide any dividends at all. Great for the children, not so great for the surviving spouse.
However, as Trustees, you are required to take the interests of both parties into account (unless the will says otherwise) when deciding what to invest in.
This would normally be done by selecting a mix of investments, some of which concentrate on capital growth (good for the children) and some which concentrate on providing income (good for the surviving spouse).
I really would recommend that you speak to a qualified advisor about this.
Then, when the surviving spouse finally passes away, the assets of the Trust can then be passed out according to the will.