Downsizing the current family home and buying a new, smaller one in the future is easy to model in Voyant Adviser. You will probably wish to model this in a What If, so your clients can see the potential outcome.
First of drag and drop an event on to the timeline in the year your client wish to do this.
Then go to Property/Assets and select the existing home from the ledger on the right of the screen. Then, in the time panel select the Start event (so a green dot appears next to it) and the newly created Downsize event (so a red dot appears next to it).
The software will sell the property at this event and the proceeds will show in Lets See>Cashflow. If it's linked to any mortgages these will be repaid at this point too, with the net sale proceeds swept into the default cash accounts.
Now, create a new property to buy in the Property/Assets section. It is important that the New Purchase option is ticked.
Then in the time panel on the right, select the Downsize event (so a green dot appears next to it) and Mortality event (so a red dot appears next to it). The new home will be purchased at the Downsize event and only liquidated at mortality.
The amount entered in market value will escalate by the default inflation rate until the property is purchased. If your client only wants to buy a property for say £350 000 at this future date then select Advanced Settings>Details and select Future Value.
This is how it is represented in Lets See>Cashflow. The spike being the sale proceeds of the first home and the black total need line including the new purchase.