You may be on the right track, generally, but you really should consider using a tax professional for this tax year (or, rather, tell your daughter and son-in-law to do so).
https://taxexperts.naea.org/listing/service/individual-tax-preparation
Actual preparation of tax returns notwithstanding, there are issues with taking a (reasonable) salary for your son-in-law as well as quarterly withholding (Form 941) which might not have been done.
Since this is California, there are likely also state issues.
Guidance from a local tax professional would be highly recommended in this instance.
