"Heres the issue. How does the will work in this scenario? Do my children inherit 85% of the house and 50% liability of the remaining mortgage? I don’t want my future husband to be stuck paying the entire mortgage and not be compensated for that? Will the declaration of trust be followed as it is described if I die?"
OK, to answer some of these questions (not necessarily in order)
"I don’t want my future husband to be stuck paying the entire mortgage"
The answer here is term life insurance. Just go and search for "mortgage life insurance" and any good comparison site will give you a whole list of insurance companies that provide this.
It's generally cheaper than ordinary life insurance as the amount insured decreases over time as your mortgage decreases.
If you already have life insurance (large employers also often provide "death in service" benefits as well) then work out if you need extra on top of whatever life insurance you already have.
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"Will the declaration of trust be followed as it is described if I die?"
This one is simple. Yes.
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"How does the will work in this scenario? Do my children inherit 85% of the house and 50% liability of the remaining mortgage?"
With the mortgage, you and DP will be "jointly and severally" liable for paying it. What this means is that the bank can hold either one of you liable to pay the full amount, not just your 'share' of the debt.
So, if you were to die then 100% of the remaining mortgage would fall to be paid by your DP. If this will cause financial hardship then I would suggest, at the very least, if you do not have any life insurance at all then to think about getting mortgage life insurance to pay off the mortgage.
With inheriting the house, this is a very common situation indeed and any solicitor who deals in writing wills will be used to this.
Typically, your will will be written so that your share of the home is put in trust after you die for the benefit of your children (or anyone else that you want) after you die. It will also say that your DP has the right to live in the home until he dies - or other event that you state (eg remarriage or cohabitation etc or a fixed number of years).
So, what this means is that your DP will be able to live in the house as long as he wants (subject to what the will says) but he cannot touch your 85% share of the house.
When your DP eventually dies the executors will sell the house and divide up your 85% interest in the house according to your will.
In case you're wondering why your share is left in trust, 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 85% 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 85% of the house and your surviving DH owns the other 15%.
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.
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As to a prenup. Prenups are not automatically enforceable but are enforceable at the discretion of the judge. They can help but you really do need legal advice specific to your circumstances from a family law solicitor experienced in this area.