If you add your daughters to the deeds of the flat you live in, you will effectively be gifting them a third each. If you do that, you will be making a disposal for Capital Gains Tax purposes at the open market value of part of your home but there should be no CGT to pay as the property is your principle private residence.
You would also be making a gift for Inheritance Tax purposes and under normal circumstances, so long as the donor (you) live for at least seven years after making a gift, its value will not be included in your estate for IHT purposes. However, should you continue to live in the property, the gift will be a gift with reservation of benefit for as long as you continue to live there and the IHT clock will not start ticking until you move out or start to pay a market rent. If you live in the house until your death, its value will remain in your estate for Inheritance Tax purposes.Take a look here
for information on gifts with reservation of benefit and here
for information on passing on your home.
The same CGT scenario would apply to the let property except for the fact that any "gain" you make will be subject to Capital Gains Tax. Given that you are in the process of buying it, adding your daughters' names to the deeds now will mean that there will be no gain. However, there will be gifts for Inheritance Tax purposes and you will need to live for at least seven years after making the gifts to ensure the value of the gifts was not included in your estate for Inheritance Tax purposes. You would be able to split the rental income in whatever proportions you liked for tax purposes.
You might consider taking out some term assurance to cover a potential Inheritance Tax liability. As taper relief (see here
) can apply to gifts after three years, the level of the life cover could be reduced as time passed. It would terminate after seven years. The policy could be written in trust for your daughters to bypass your estate. There is some information on term assurance and IHT here
I hope this helps but let me know if you have any further questions.