1There is no reason why an existing trust cannot be added to as you will see in example 3 here
. You both appear to be settlors of the trust. An increase in the trusts value will affect the ten year IHT charges. There are some HMRC notes on discretionary trusts here
2 A gift to you by your wife of her half of the property is a disposal for Capital Gains Tax purposes but as you will take her share of the original purchase price as your own, there will be no gain or loss. Gifts between spouses are normally exempt from Inheritance Tax and are not treated as potentially exempt transfers.
3 Take a look under the heading "Making Gifts" here
. It is possible that HMRC could level the "Ramsey" principle at you if they saw the gift to you of your wife's share of the property to you followed by the gift of the property into the trust as a series of transactions designed to avoid Inheritance Tax. It may be that it would never be enquired into. A delay of a year or so after the transfer to you may serve to avoid a close inspection by the tax office but there are no guarantees.
A while back, tax consultants were advising spouses and civil partners wishing to put property into joint names before a disposal to save CGT to make the transfer into joint names and the sale occur in different tax years to avoid HMRC accusations of tax avoidance. However, HMRC made a statement stating that they would not seek to challenge such transactions so that may give you some comfort.
I hope this helps but let me know if you have any further questions.