We were married in 1967 in another country, in the 80's I filed for divorce due to maltreatment , we never separated stayed living together and continued filing joint returns it was a joint decision not to separate. We had joint property before the divorce and during living together, how can we part with ownership and is it costly, we are now ages 69 and 70

You are divorced, so you will have to just agree to who owns what, and divide it without the court

You illegally enjoyed the benefits of joint tax returns... but even if you were divorced in the US, the IRS doesn't know this unless someone tells them.

I agree that property settlement is between the two of you. Hire one legal mediator if you want to save on two lawyers. Save even more and work it out on your own! Make lists and take your time. You've gone this long so why not do this peacefully. At your stage, the two biggest obstacles are who gets the house and who gets the pet(s) if any.