Hi. My name is*****'m looking at your question now and will post my answer or ask for more information here in a short while.
You can mention that the property was jointly owned in box 38 of page CG2 of the Sa108 pages here. However, you each need to disclose your respective shares of the gain in your respective tax returns and provide HMRC with a calculation of the gain. If you use the HMRC tax return software, there is a worksheet you can user which does all the work for you in that it produces a PDF document in the format that they want. You just populate the boxes with the facts and figures and claims for reliefs. See page CGN3 of the notes here for the relief codes.
I hope this helps but let me know if you have any further questions.