Technically your personal items and liability would be covered under your parents' homeowners insurance policy while you live under their roof. However, if you had to file a claim you would be doing so under their policy.
Coverage & Claims
If you have collision coverage on both policies then it is likely that the damage will be covered. However, since you two are married your liability will not cover the damage to your husband's motorcycle since you are not unrelated third parties.
Your best bet is to contact an attorney. You may even consider contacting the police department, but I would recommend contacting a legal representative first since an attorney should be able to assist you in getting this other party to cooperate. You wouldn't be able to file a claim for the vehicle since you technically never owned it so legal representation would be my recommendation.
Assuming that your son and daughter-in-law maintain a homeowners insurance policy of their own, it would not be necessary for you to add them to your policy. Their personal property and liability will still be covered by their home insurance provider while they are staying with your temporarily.
You could always claim the accident as if you were driving but I highly recommend that you avoid lying to your insurance company. If you file a claim, they are going to want to know what happened so there won't be any way to avoid involving your friend other than being dishonest.
Coverage & Claims
Anyone listed as a driver on the policy will be covered to operate the vehicle for personal use. If a person lives with you, drives the vehicle on a regular basis, and isn't listed as a driver on the policy then they are definitely not covered to drive.
This can be a bit confusing your first time around so I should be able to help. Your best bet is to first determine which vehicle you will be purchasing.