My daughter Elida married a young man from Guatemala and I have no information about where he came from. My daughter passed away a few months ago leaving 2 little children. I want to find his famiy history and all I know is that he walked from his country at age 12 all the way to the USA. That his family are dirt poor and his father has passed away. Nothing more. Any ideas please? Can't ask him more now as he is out of his mind with grief.
The only way to trace your family history is to start with what you know and work from there. In some cases, if you don't know enough, there is no way you can get anywhere – but you can't know until you've tried.
Presumably you know your son-in-law's name, but it sounds as though he has a very common surname, so that's not much help in narrowing things down. Small details like birthdays, even if you don't know the year, can be important to note.
He married your daughter, so there presumably is some record of the marriage. Depending on the location of the marriage, and the requirements of that jurisdiction, that marriage documentation may provide some important details – age of your son-in-law, possibly parents' names, possibly birth place. If they married in the USA then I would be optimistic that the marriage record may contain useful information.
Don't start searching in Guatemala before you have some concrete information to go on – it will be a fruitless search.
Keep in mind that there are likely privacy restrictions in place which may not allow you access to certain records of living persons. This will depend on the jurisdiction. Also be mindful that there are social and political reasons that might make the search more complicated; an undocumented immigrant may have changed his name or falsified details, or simply not appear in records you might expect.
My advice would be to give your son-in-law some time to grieve before pursuing his genealogy. Your family history is not going anywhere, but when he is ready he is really the best source of information you can possibly have.