Hello firstly let me say I am sorry to hear of the loss of your BiL and the position you find yourself in I have been following this thread quite closely as I am in the process of trying to set up a complete home workshop.
I have watched many MYFORD lathes sell on eBay while I was looking for a lathe for myself and they have always sold very well because they are a very attractive option as a very reliable and well made lathe with many additional Myford made accessories available as you have found out yourself.
They seem to come in various guises (and I am not an expert here) from a basic 7 to a super 7 and ones with added clutches etc etc etc, the one you have is quite obviously at the very top of the tree with a gear head fitted and powered cross slide,I have not seen one of these sell before so cannot say I have seen one of these sell for lets say £2,800.The ones I have watched generally sold from £1,200 to £1,700 which is easy to verify as there are generally a few for sale.I personally was put of buying one by the pure weight of them and the difficulty moving them.This may alert you to one of the problems you have in the fact that yours is situated in an up stairs bedroom, getting a MYFORD SUPER SEVEN with gear head out of an up stairs bedroom and down to ground level is no mean feat, which also applies to all the other weighty things you have.I personally think this would put off a lot off potential buyers, if you consider what your market will be for the lathe it is probably someone like myself wanting to set up a little home workshop probably for the first time with a limited budget, unless of course they have bottomless pockets, another buyer of the lathe might be someone that already has a workshop and would like to upgrade his basic lathe to something better this will be someone that knows the score as far as moving such things about, ie dismantling said lathe with a helper to get the lathe out and any other problems that might be.I think this would probably affect the price he would be willing to pay. Selling the lathe with all the various accessories that you have will make it a far more attractive proposition to anyone buying the lathe but don't expect that person to pay top dollar for all these extras, and why would you want to be left with all these things to try to sell separately.
I would say if that's what you want to do try to sell the accessories first and see what reaction you get to them at the end of the day something is only worth what someone is prepared to pay for it.
In my case the lathe I bought I had to go and pick it up, a round trip of maybe 160 miles but the lathe was situated in a large garage and had been placed directly behind the large shutter doors so it was a doddle to reverse the car up and slide the lathe into the back.The gentleman selling the lathe on eBay had put very little info about the lathe and had started bidding at £1,500 or make an offer which is what I did there were no other bids at all so it looks like start low and set a minimum reserve and see how it goes.
I hope this may help you in your efforts to dispose of the workshop for your Sister in Law
john