What type of visa? ?

Try the Hail Mary visa if they want to lose the 160USD per person as they will not be given any visa.

It would be a tourist visa but it's unlikely they'd be approved. From Baja to the Yucatan there are parts of Mexico that aren't currently under State Dept. travel warnings. Pick one of those and marry there so your future in-laws can attend. 

I don’t think it’s a good Idea to get married in the USA, because there is probably a high chance your parents in law would get denied the visa. Why don’t you and your fiancé get married in Mexico instead ? He has no problem seeing his family since he is a US citizen. 

They're not staying; so they'd need to apply for tourist visas.Given their history, there's a 99% chance this would be denied.

If you want his parents to be at the wedding then marry in Mexico as they will be denied a visa of any kind with a history of visa fraud

There is absolutely no chance that they will get avisa. Get married in Mexico.

If you feel it is important for your fiance's parents to attend the wedding then you will need to have the wedding in a country other than the USA. 

With their records of illegal immigration, fraudulent asylum claim, and deportation, they are not returning to US. They won't get any tourist visas. It would be total waste of $160 each to file any application as they will be denied. If you two want them at the wedding, get married in their country. 

i would ask immigration about it

Normally, they would come on a tourist visa. But I think there's very little chance of that happening with their history. They need to talk to the people at the consulate.