Visa For My Vietnamese Fiancee To travel to China/Hong Kong & Macau

Hi,
Myself and my Vietnamese Fiancee are planing a 4week tour of China/ Hong Kong & Macau in April and I'm wonder what the easiest way is for her to apply for her Vosas ?
Would we have a better chance of approval if an agent did all the work or are we better off just doing it ourselves ?
I'm going to be in HCMC at the beginning of March ans we're hoping to sort everything out then.
Last Q: How long shall the three applications take to go through the system ?
Thanking you in advance. Geoff.