My son in law is a learner and is named on daughters insurance, can he drive my car?

When it comes to learners, insurance becomes a really delicate thing. Some insurers allow the 'drive another car with owner's permission' on some comprehensive policies but I'd think this wouldn't stand for a learner because the risks are greater. However it is better to ask your son-in-law to contact his insurer (or your daughter to call them up as she's the policyholder I believe) to clarify on that matter but I'm inclined to think they wouldn't allow this.

If the response comes out negative, then you can try to add him onto your car insurance or even better get him a learner driver insurance policy which is short term (eg a month) so that he can practice in your car as well as your daughter.