1. Beneficiaries question first - current law provides a step up in basis to date of death fair market value. That basis step up is supposed to be pushed down to your share of the partnership, if you give them the facts. That would reduce K-1 income to the beneficiaries as well. One of Joe Biden's proposals is to eliminate the date of death value step up. Talk to me after the Georgia Senate runoff elections in January and maybe we'll have a better idea of how likely the change is.
2. Selling your 2008 EPD/MMP units will presumably generate a ton of ordinary gain but you should also have a lot of capital gain as well. I suggest asking your accountant (unless you can do this) to check on K-1Support or other site for an estimate of the ordinary gain. I wouldn't hurry to sell just to offset your capital losses - any unused capital losses this year will simply carryover to 2021 and you can also sell some gains in 2021 to use up the losses. Your ordinary gain should qualify for the 20% QBI deduction if you sell the units this year. Next year? Again, wait for the Georgia Senate runoff elections to see if the QBI deduction survives.
3. I have no idea of your income level (and I'm not asking) but if it matters, think about the impact of the ordinary gains on your Medicare premiums next year.