Are joint tenancies ever advisable?

In some cases, yes. However, they are rarely the best method of holding property. Only a lawyer is qualified to advise you on the best method of holding title to property and your case will differ from every other case.
The matter of joint tenancy involves many very difficult problems. Usually property of considerable value is involved, often all the property which one or two persons possess. Only the lawyer is specially trained and licensed by the state of Oklahoma, to advise on legal problems. See a lawyer before, not after, you are put to trouble and unnecessary expense.