I want to purchase a second property in Manchester for me and my wife to live in. However, I already own a property held jointly with my brother and which is currently rented out. Unfortunately, I am caught out by the stamp duty land tax (SDLT) rule changes introduced back in 2016, but want clarification if I will have only to pay half of the SDLT due on the purchase of another property. The second property will be purchased jointly with my wife (who does not own another property) and she will be on the title deeds as well as the mortgage deeds. Are married couples treated as one unit in regard to purchase of a second property and hence a liability to pay the SDLT?  

See www.gov.uk/hmrc-internal-manuals/stamp-duty-land-tax-manual/sdltm09820 and SDLTM09766 that the full extra 3% SDLT will apply to this purchase, because all the four conditions are fulfilled by you, and a married couple are looked upon, for these rules, as one unit (I presume that your interest in the first property is worth more than £40,000; see sdltm09780).