There is no way in this scenario with children this young I would split everything equally three ways.
Your Dd has only you to inherit from. However if anything happened to you, you need to ensure that your partner has the money to look after / care for her. So typically what would happen is your assets would go into a trust. That would be managed by trustees. And they would release money to your partner to help meet costs of raising/ feeding/ educating her.
At the age of 25 (I recommend a higher age), the trust gives the child the money that is left.
That is how I would set up anything for my assets pre marriage for my child in your relationship.
As many others have said, if anything happens to your DP, the children will be cared for by their mother. His estate should then provide sufficient funds to maintain child maintenance until the youngest is 18etc and as many others have said, people often take out life insurance to provide for this so claims are not made against an estate.
If you think that once people sadly die, their wishes are carried out regarding their money, you would be sadly mistaken. I know of times where money has been left to a partner who promised to treat all children equally. They have then met someone else, remarried and subsequently spent what should have been a child’s inheritance on funding their lifestyle. I’ve honestly seen some Horrible real life examples of people completely reneging in agreements made while a partner/ child/ sibling was alive.
Don’t do that.
Re any joint property that can be set up as tenants in common. So both of you have a right to remain in the house until you both die. At which point the shares revert into individual pots for the trusts for the respective children. I’m sorry but if I paid 50% into a property, that 50% would be going back to my child. Not 33%.
I think it’s admirable when people say let’s treat all the children equally. But that isn’t necessarily how things end up.