Shenzhen, scouting visit

Hi, this might be complicated so I'll keep it as direct as possible!. My family and I are all British passport holders and we are all moving to SZ in July on a 3 year contract. We are in Hong Kong over Easter and would like to scout out the area where we'll be living and working. We only plan on going for the day, maybe overnight.

Complicated bit.. My wife and I recently married and I changed my surname to match hers. My passport is only a week old and the previous passport was not returned due to a name change. I still have my ‘previous’ ‘previous’ passport, expired mid 2017 so can bring that and our marriage certificate. My wife's passport is just one year old as is my daughters. They can bring their previous passports.

We have never visited China before so what are the odds of getting a visa upon arrival? If this is low are there quick ways to get a short visa whilst we are in Hong Kong?

Many thanks!