Does anyone know of any aromatherapy that would help diabetics relieve stress and is there anything that can be use for rhuematoid arthritis?

Not Aromatherapy but there are some good herbs that can help.

My favourite essential oil for stress relief is neroli.. orange blossom essential oil, however this is quite expensive. I could however recommend to you to buy one of those little orange trees that are grown in the home with the tiny oranges. The blossoms from the oranges are what makes the essential oil and give off a very nice scent. Neroli is used by aromatherapists for extreme stress as well as grief. For an very uplifting blend I would highly recommend 3 drops of Bergamot and one drop of neroli in a diffuser (aromatherapy burner). Fill with water (about 75 ml.) then add the drops. Light the tealight underneath. The tealight will burn out around the same time as the water has burned off.
As for the arthritis I would recommend that you seek out a qualified aromatherapist and make an appointment to speak with them. They will find out all they need to know about you and make you a blend for arthritis. Since all of us are individuals, some things work better for some than others. Also, as in herbs, a change up of blends is always a good thing, as the body gets used to one thing and the effect is not as good after a while.
An aromatherapy massage has to be the best kind of treatment in the world as far as I am concerned:)