My boyfriend (Spanish) and I (Chinese) are traveling to Hainan for 14 days.

I would not suggest you that he relies on Hainan VOA. On this website, there is still posted a case of three UK citizens denied the plane boarding because they didn't have an invitation from a local tourist agency from Hainan. In other words, all those who plan to travel to Hainan are supposed to rely on 30 day visa free access and not on Hainan VOA.

Your boyfriend should start a correspondence with one of the local Hainan travel agencies that have an English speaking staff. It is easy to find one just by using an internet search and by inserting "Hainan agency English speaking" phrase in the search engine. During the correspondence, your boyfriend will declare the address of your family and also confirm that he will be staying exactly there and in the same time enjoy Hainan and explore it with your guidance. This is just fine. The only detail he will have to do is to accept one simple service from the agency like an airport transfer. This will bring him an official invitation that he will print out and use for travel to Hainan. As you can see, this procedure will ensure him that he will be allowed to board the plane, to enter Hainan and to enjoy his time there without the need to obtain a visa. This procedure could appear to be somewhat complicated, but in reality it is not because the agency is doing its part very fast and everything is done within 4 or 5 working days. Usually, even less than that.

You can insist on Haian VOA and maybe you will be successful, but if I were you, I would not do that. The real and definitely safe option is 30 day visa free access. Please, do yourself a favor and travel with complete peace of mind.