Shy and Aurora have a point. If they were truly gifts, and he knows that, and you have corroborating witnesses (i.e. your children if they were there, friends, etc.), his demand wouldn't stand up in a court of law. I must also agree with cutting out any and all contact, for both your sake and the sake of your children. He does sound highly unstable, and quite possibly like the sort of person who would try and drag them into a fight. I would say get a restraining order, however, depending on where you live those can get expensive ( I know over in Dallas, TX, USA the various fees and lawyer stuff has a going rate of $500). If you cannot afford that (like I said the cost appears to be highly region dependent, and I'm speaking only in terms of the US, I cannot speak for anywhere else), then do as Aurora mentioned and call the cops, see about possibly having watch around your neighborhood beefed up, especially as it seems like itwouldn't be just you he'd cause issues with, but anyone who got in his way. If you can't get that, then talk to any and all friends you may have in that region. Keep them abreast of the situation and set up something to the effect of an "emergency switch" (not it's true name, but close enough) with one of them ( basically an arrangement to contact them by/ at a specified time each day. If this hasn't happened within 'x' hours of when it was supposed to, and they can't reach you, they are to call the cops and say that it's possible your father is involved in your disapppearnace. If the cops are already aware of the situation ( at least the ones that work your area), this will help them immensely in figuring out what has happened.) I know this sounds extreme, I do not intend to scare you. However, if he is as threatening as you make him out to be (and I have no reason to believe otherwise), this a good idea. I've done the "emergency switch" before, both being the caller and the callee. It helped a good friend when an ex was stalking her. Depending on how old your children are, I would also say keep them briefed. Not necessarily knowing the whole ins and outs, but enough to know that Grampa is no longer trustworthy.
Like I said, I know this sounds extreme, but if you trust these friends/ family members, it works beautifully. As for false alarms, believe me, the cops would rather have one or two of those only to find out you're safe than to call a search for a family disturbance diappearance.
23 year old female with depression, allergies, and minor anxiety disorder. On Welbutrin and allergy meds.