How best to help my Son and wife in purchasing.

Just an FYI, but I've been approved for a mortgage while in a jobs probation period. There is some leeway depending on the industry and time between jobs.

Also most probation periods are 6 months. Assuming they are already back in the country and month or two, it'll take them at least a month or two to find an area they like and a house they like there, then the buying process is usually at least another month, all of which will push them very close to the end of the probation period.