Muniment of Title does not get you letters testamentary, and from what you describe, I can't tell where you are in the process and what needs to be done. If the lawyer is not available after paying $15000, then find another lawyer. You need a lawyer's guidance. This is simply too complex to answer in this type of forum without a face-to-face interview.
I think the language you quote is pretty clear. The car identified doesn't exist, so that gift lapses. You don't substitute another car for the one described. The car that does exist, unless gifted by another bequest, becomes part of the residuary estate and goes to the person identified in the second clause that you quoted.
This could have been clarified by probate, which I gather didn't occur. Regardless, you possess the item, they claim it belonged to your mother, that it then should be theirs (I don't know why). But, it is too old to open an estate, and you aren't legally or ethically obligated to turn it over to them. You do not need to surrender it to them and they can not get a court order to make you do so.
Well, happy Thanksgiving!? Sorry these issues burden you today and I apologize for this necessarily vague answer. The issues here depend on the ownership of the property (was is community or separate) and the terms do the deceased husband's will. The will may purport to give to the son property belonging to the widow, so the will may not be what it seems. But any decent answer requires an understanding of the assets and examination of the will at issue. Please have your mother in law...
Really making some guesses here, but a deed doesn't have to say "$10 and other good and valuable consideration." It can be "granted per terms of ___ Trust" or "gift per Will probated . . ." j
It sounds like the Trust owns 1/2 and your sibling owns half, if so, both the trust and the sibling need to grant you all of their interest, not just 50%. Really, need a title report and the deed to do this. Ask these questions to the lawyer preparing the deed.
If your father died and left all to his wife, then you are not automatically entitled to anything from either estate. You would have to challenge your father's will and you've described no facts to support a challenge.
As to the "stuff" this is a classic case of what I call the "pickup probate." Which means: the first one to the house with a pickup wins. Cruel, but true. Yes, you can sue your grandparents and uncles, but pursuing such a case won't be worth it. If your father died unmarried and you are his only child, then you are the heir. You refer to probate of a will, so the will controls and an executor should be named. I'm assuming the uncle is the executor and he is correct, the bills must be...