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The important aspect of his separation, is whether he has settled the property with his ex-wife. If he has signed a properly witnessed relationship property agreement, then there is no possibility of any claim. In your present situation the house you are buying together is separate properly. If he has not completed a property agreement, and the funds he is putting into the house come from relationship property, then it is possible that his ex-wife could apply what is called tracing to make a claim against the money, and the money invested in house. If the deposit to buy a house is based on income he earned after separation, and there is no money from the formal relationship, then this house is separate properly.

The issue of protecting against any claim if he passes is important to consider. Again, this depends on whether he has completed the relationship property settlement with his ex-wife. If this has been signed off, then she would have no claim against the property. And if there is no agreement with the ex-wife, and the relationship property from the marriage was used to purchase the house, she may have a claim.

There are a number of ways to protect the property. If you own property as joint tenants, then passes to you if he dies, by what is called survivorship. You do not need to do anything for this to be the position. Matters can get complicated if there are family trusts, and in this answer I have outlined a number of what it positions. Please feel free to ask any clarifying questions.

The liability for child support ceases if he dies. There is nothing in the Child-Support Act which would entitle some lump-sum claim for child-support. There is a possibility that children could claim under the Family Protection Act, but of the property was held as joint tenants, it would pass to you by survivorship. They could not then make a claim. If he has provided for them through the trust, then that would discharge any duty he has to provide for them.

Yes-provided there is an agreement with her about property.

go for it

Your will should state who the guardian will be after you die, and this is usually the end of any argument. In addition, at 14 your daughter will have views on where she would stay which would be taken into account. Your present partner will not be liable for child support, as her father will continue to have that responsibility. But you could not stop your mother challenging the guardianship, although the chances of succeeding, where you have a clear guardian appointed, and your daughter wants to live with the guardian, are very low. Your mother would have no property claim. It is only descendents who can make such a claim. So the key is the appointment of the guardian, and for a 14-year-old, I would recommend some discussion with her.