A picture of the trunk would be more useful. From your description I think the rampant thorny branches are likely to be rootstock and should be removed as they are taking the nutrients from the graft and the fruit. Citrus grafts are usually higher on the trunk than other fruit trees. Al

Trees and other plants are not an exact science or our jobs would be easy. We look at all research, make the best decision we can, and hope what we do works. Even a tree that is perfectly planted and cared for can; though rarely, develop girdling and nasty cross roots. OP said that most of the trees he was concerned about are young which gives them good chance of recovery with root treatment. Sure the OP may loose some trees to the root surgery but left alone with the problems he described they have little chance of growing up to be nice trees. I have worked with both scientists, businesses and the public and scientists do work in a different thinking zone. They present facts that in science are definitive to them, that is just the way they think. The research that they do has to be used and considered by us, but is not always practical to the real world in which they do not live.

Personally, I recommend going own root. I've found that potting small own root roses in one gallon pots then moving them up to a larger pot, before planting in the ground, gives me a larger plant sooner. My last summer's rooted cuttings overwintered in a cold frame in my unheated greenhouse and repotted into one gallon pots in March are almost full sized plants. It's said that crowding the roots gives a bigger plant sooner. Instant gratification with a grafted rose is not that important to me. I'd rather wait a few months for the own root to catch up.

Cool! Go for it! Budding, rooting, layering are all skills we're losing daily. Add to them baking, weaving, needlepoint, knitting, bread making, canning...we get farther and farther from doing anything for ourselves and more helpless every day! You will find the bark on the multiflora easiest to lift and separate from the cambium layer when the sap is flowing freely. That's when new growth is pushing from the plant quickly enough to almost SEE it grow. That isn't going to happen under grow lights inside. You may try your cuttings indoors, but to have the greatest success budding, get them outside and actively growing. Again, not to sound condescending, you are familiar enough to know to take the cuttings approximately the same gauge (diameter) as your bud wood? You can't bend the bud much and expect it to succeed and you can't have it sticking out of the "T" cut and have the cambium layers knit together. Probably the easiest thing to do would be to cut six or so inch long shoots the approximate thickness of what you wish to bud to it. Take a sharp knife or a razor blade and cut out the growth buds at the leaf axils, remembering there are three buds there, even though you can only really see the middle one. Remove all but the top one or two from each cutting. From there on, you strike them using whatever method you've had success with previously. I won't dare try to tell you what to do because you very likely know what works where you are a whale of a lot better than I would! I just wanted to make sure the odd things you would do for a root stock would be covered to enable you to succeed your first time! Take the mystery out of it and it is SIMPLE! Good luck! Let us know how you do! Kim