Remove side growth from graft joint on new grafted avocado?

[pg]

Recently picked up a small grafted 'Fantastic' avocado off the clearance rack at Home Depot, and once I got home I realized about 2/3s of the lush, vigorous growth were coming off two branches coming out of the side from right on the graft joint.
I'm guessing I'm not so lucky for this to be growth from the scion... I should cut these branches off, correct?
https://postimg.cc/gallery/MGtpH4s

Also, I've read 'Fantastic' should be hardy to zone 8b, but it's likely on a less cold hardy rootstock? Any idea what the rootstock may be? The plant is from Florida. I was wondering if I cut those two lower branches off, would it be worth trying to root them, either to grow as is, or to use for future roostock? I'm growing some seedlings anyway, so why not, right?

[drymifolia]

That looks like a side veneer graft, and all those branches look like they are from the scion to me. In fact, the top branch is the one that seems like it might be from the callus rather than the scion, which could be a graft chimera. But I don't think so, pretty sure this is the graft union:


There's an easy way to test, though (assuming the scion is actually Fantastic and not a mislabel): crush a leaf from each branch under your nose. They should have a strong anise scent. The rootstock is likely a Lula seedling, with no scent in the leaves.

[pg]

I had just assumed the vertical part was the true scion since it was the one tied up to the stake. The leaves look very slightly different to me but I'm not sure, could just be due to not being as fresh and vigorous.
I crushed up a leaf from the side branch, and it definitely had a strong anise scent to it. From the vertical branch I think there was a slight scent somewhat spicy but not as strong, however I crushed up an older leaf since there's less fresh growth on that branch.
Here's another image showing the leaves: https://i.postimg.cc/Pq8SYBvV/top-view.jpg

[drymifolia]

I had just assumed the vertical part was the true scion since it was the one tied up to the stake. The leaves look very slightly different to me but I'm not sure, could just be due to not being as fresh and vigorous.
I crushed up a leaf from the side branch, and it definitely had a strong anise scent to it. From the vertical branch I think there was a slight scent somewhat spicy but not as strong, however I crushed up an older leaf since there's less fresh growth on that branch.
Here's another image showing the leaves: https://i.postimg.cc/Pq8SYBvV/top-view.jpg

If the top branch is a chimera, it could be interesting to let it grow, but you might want to remove it if you don't want an experimental project. It does seem to be coming from the callus, but the leaves look pretty similar on all the branches to me. Anise scent is usually strongest on hardened leaves, not young leaves.

[pg]

The vertical branch doesn't seem to be detrimentally affecting the more vigorous lower branches, and I was more worried about the inverse issue, so I'll let all three remain and see how it goes.
Thanks for preventing me from butchering the poor tree!