What kind of visas will we need for a trip to china

If I have properly understood, your flights will be: UK - Hong Kong - Guangzhou - Vietnam.

In this case, you are qualified for 72 hours visa free transit in Guangzhou, but you can travel through the entire Guangdong province. Keep in mind that 72 hours visa free actually activates the day after your arrival at 00:01. In other words, in case that your flight from Hong Kong to Guangzhou arrives in the morning hours of Monday, your visa free stay will be activated at 00:01 on Tuesday. Like this, you will have Monday, Tuesday, Wednesday and you have to depart from Guangzhou by plane to Vietnam at the latest on Thursday at 23:59.

In case that you intend to stay longer in Guangzhou and the area of Guangdong province or if you intend to enter mainland China toward Guangdong by train or by bus or you intend to leave mainland China overland to Vietnam, you will have to obtain Chinese visa in advance.

You do not need any kind of visa for Hong Kong. As far as Vietnam is concerned, your husband can travel to Vietnam visa free for 15 days, while you have to apply for Vietnam visa through eVisa system. In case that you will stay in Vietnam more than 15 days, then both of you have to apply for Vietnam visa through eVisa system.

I think they want to fly UK > HK > Guangzhou > HK > Vietnam which needs a visa. Travel from Guangzhou > Vietnam must either be non-stop or fly through a country other than HK.

It is quite possible that they have in mind exactly what you have written. Anyway, they will read this and appear here again to clarify the details.