"Their thinking is then only 50% would be considered for care home fees and the other 50% would stay with other spouse. Is that how it works?"
The first thing to be aware of is that care home fees will only be an issue for the surviving spouse that goes into care.
If you are married and go into care then the value of the property is disregarded if your spouse or a range of relatives, such as children over the age of 60, are living in the house.
In that case the value of the house is disregarded when calculating liability for care fees.
The issue comes if one spouse dies and then the surviving spouse goes in to care.
This is where this will protect 50% of the home from care fees.
Most homes are owned by a couple as "joint tenants". This is where you both jointly own the whole house (just like a joint bank account). So, when one of you passes away the house automatically goes to the surviving spouse. In Scotland, I believe this is a called a "Survivorship Destination"
If you own the house as joint tenants then the house automatically passes to the surviving spouse regardless of what any will might say.
So, if your DH were to pass away first then you would get everything and it would be quite open to you to get involved with a younger gigolo and then leave everything to your young lover (or the local cat's home charity etc) when you eventually pass away so that your children get nothing.
I'm sure that you wouldn't do anything like that but you do read stories on MN about that happening.
Likewise, you could pass away first and then your DH remarries and leaves everything to his new wife. Again, plenty of stories on MN about this as well.
However, given that your DP are in their eighties I guess that there's little chance of either of those things happening!
.
The other way to own a home is as "tenants in common". In this situation you each own a separate 50% of the home and you can leave your own 50% to whoever you like. In this situation it is usual for each spouse to leave their 50% to their children (but you can leave it to whoever you like).
So, if your DH were to pass away first, then you could still give your 50% of the house to your gigolo but you couldn't give your DH's half of the house to him. Likewise if you were to pass away first then it would protect 50% of the house going to any new wife.
In the same way that 50% of the house is protected from any gigolo or fancy woman (or cat's home charity) like this it is also protected from being taken for care fees.
In Scotland I believe that the equivalent of tenants in common will have the phrase "equally between them and to their respective executors and assignees".
.
"I’m not sure all the implications of this eg: does the remaining DP have the right to stay in house given they own only half; could be a DC force a sale to get cash out;"
In the will, each 50% of the house is left in trust to the children. The reason for doing this is largely to protect the surviving spouse from being turned out of the home.
There is nothing at all to stop you leaving your 50% directly to your children. Assuming that they're over the age of 18 then your share of the house passes directly to them in your will.
This means that they own 50% of the house and your surviving DH owns the other 50%.
They can then get a court order to force the sale of the house and turn your DH out. (or vice versa if you're the surviving spouse).
The trust stops this from happening. It says that the surviving spouse has the right to continue living in the house until his death (or other event mentioned in the will eg remarriage). This stops them being kicked out of the house by the children.
"...could be a DC force a sale to get cash out"
No, and even if the surviving spouse wanted to downsize which would release some money then the DC are still not entitled to that money at that time. It must be invested until the surviving spouse passes away (and they get all the interest and dividends rather than the DC).
"could a DC block a sale if the remaining parent wants to sell up (eg downsize to retirement property)?"
No, but they may not have to contribute towards a new home. It all depends how the trust is written. If it is written by a competant solicitor then it will likely say something like the Trustees should have regard solely to the interests of the life tenant (or Liferenter in Scotland).
If there is any money released at any point from the sale of a property than that remains within the trust and must be invested.
"If they sell would the DC be due CGT as it’s technically a second home of theirs (part small ownership)."
No, the property is basically treated as though the surviving spouse owned it during that period. CGT will only be relevant if the surviving spouse spends more than three years in a care home (or 9 months if the house is let out while they're in care) and the house is not sold during that time.
Also, as others have said, this is not deprivation of assets.