Before the leaves even come out, you can tell the two of them apart by the colour of the flowers from a distance. Red elms have a red haze of bloom when you are not too close. White elm (american elm) have a pale green haze of bloom. Also, red elm blooms a week or two before whites. Re the resistant ones, yes, if you can only have few trees or even one in your yard, get one grown from cuttings. it will exactly copy the original. if you have a large woodlot and want to introgress resistance genes, plant seeds from some of the resistant ones and let nature cross them up. Also, resistance is showing up in local older trees, but finding them is the issue.

I have several wild American Elm growing on my property near Waco, Tx. I still have at least one of these potted (about 2' tall). IF someone wants it, I will send it to you bare-rooted free of charge up until end of April, except you must agree to post here annually its growth results and agree to at least weekly watering if no rainfall during spring -fall for first year. Our American Elm here appear to be DED- free, but the trees are much shorter than described back east. Our native Cedar Elm appear to be the better choice for here, but the few large American Elm growing only along river and creek beds do look nice. I am not an expert on American Elm, only an interested observer on the western fringes of their territory.

this is the type of tree.. you learn a very valuable lesson on ... you should not have bought this particular tree ... because of this ... and trust me.. i bought a lot of trees... before i learned this lesson ... your second lesson.. is that when this thing is a foot or 2 thick .... this wont matter ... part of you stress here.. is you want it perfect now ... and wehn pruning trees... now is not really a big deal.. most deal in centuries ... i had a situation like this.. and it took me 6 years.. to clean it up ... yes.. 6 years ... and you want to know what need be done now ... the consensus seems to be.. take out the middle one... i will leave it to them.. as to how to do it ... because i never figured out how ...... look close at the first pic ... do you see those raised areas in between the trunks... that is the fail point .. at some time in the future ... as those trunks thicken.. they will include bark.. and create a horrible crotch ... see link.. especially the 2nd and 3rd pic https://www.google.com/search?q=included+bark+in+a+bad+tree+crotch&source=lnms&tbm=isch&sa=X&ved=0CAcQ_AUoAWoVChMImdPk5ez0xwIVkxGSCh0MzA4r&biw=868&bih=745&dpr=0.9 then come back in a year or two ... just never forget ... there is no real hurry when pruning ... also ... get a good pair of hand shears ... i prefer felco ... if you had snipped this problem out.. 3 years ago .... because you saw what might come of it... then we wouldnt be here today ... gotta run ken

I agree with arbor Dave, that your examples bark looks like Siberian elm species. Except for leaves which almost look like Witch Elm because of unique "W" shape. Different types of elms are supposed to be able to crossbreed, so your tree might have that going for it. But Siberians suffer from cankers, and from wetwood which is normally only a visual problem. In any case regardless of living trees general health, structural wise it may never recover. Someone also suggested removal of dead wood, which I agree would be one option. We lost 80-100 old Siberian elms to extended drought few years back in our NE Illinois region. I am really a big fan of Siberian, but most produce a lot of deadwood which requires regular maintenance to remove. And at times, more dead wood caused by pruning event. Especially when vegetative management arborist contracted by utilities head back branches and limbs. I live in a community named Elmwood park, where several examples of mature public Siberian elm trees stand tilted. Which I had learned was caused by past village workers using auger to dig out hole for new tree, but drilled too deep. Then tree inevitably settled oddly. Mulberries also iconic for production of abiotic wetwood, which protects damaged tissue usually found between rubbing attachments from outside organisms trying to enter. As long as wet wood flows, oxygenless environment maintained. Ironically after our big drought, some trees were cured from wetwood production. Old sap wood can also contain stored water within American Elms, that pours out when stem severed after felling. Which is also supposed to create oxygenless environment that protects inner core of tree. Retaining pockets of accumulated rainfall in rotting out parts is also supposed to be more beneficial than drilling hole to drain it.