Quick answer
Your turnover from every trade and your gross property income are added together to work out your qualifying income. If the total is over the threshold, all of them come into MTD, and each one needs its own quarterly updates. You still submit one final declaration.
Adding them together
A hairdresser with £18,000 of sales who also sells online with £9,000 of sales, and has £8,000 of rent, has qualifying income of £35,000.
One update per source
Each sole trade gets its own quarterly updates.
UK property is one property business.
Overseas property is a separate property business.
One final declaration
After the year ends, you submit a single final declaration covering all your businesses and any other income.
Software
Check your software can handle more than one trade, and property income if you have it.