I would imagine the larger two trunks are rootstock and should have been removed a long time ago. Honestly, if you like the fruit from the smaller trunk (you say that's the original variety?), then keep only that one.

Thank you! Do you think it's okay to just cut away those trunks from the rootstock as low as I can (probably a little below ground level)? I want to make sure that wouldn't have a bad effect on the small trunk/tree.

Cut them wherever you can. But just be careful not to damage the trunk of the good variety! You can start by cutting up a little higher for now. Then, over time, cut lower as you have time and access. It will continue to try to regrow though, because it has a lot of mass.

Before i cut them out i would try and graft them. i second the motion they are from the rootstock and should have been cut out years ago. still, try a series of grafts on each trunk and you may get fruit. cutting them off would set you back a number of years when grafting them could result in fruit.