You mention pensions (which presumably die with her), life insurance & savings. So she had some assets. Something needs to be done to realise them, & I would have thought this is unlikely to be possible without letters of administration.
It may be that the debts exceed the value of the assets, in which case once the assets have been realised they should go towards paying the debts. If the debts were in her sole name any part of them that can't be paid from her assets has to be written off - the creditors cannot pursue you or anyone else for the money.
So far as the hotel is concerned, she had a lease. The landlord will presumably find someone else to lease it to. If the contents (or any of them) belonged to your sister & not to the landlord then the landlord should not have taken possession of them - unless there is a specific clause in the lease giving them the right to do so. If they have taken them over, it should be on the basis of a proper inventory and at a proper valuation. This value should then be offset against whatever your sister owed them in unpaid rent etc. It might then mean she still owed money to the landlord (in which case they become a creditor along with all the others), or they might owe money to her - which should be collected in as an asset. It can become even more complex if some of the items (e.g. the stock) had been provided by a supplier who had not been paid for them.
This perhaps give you an indication that it can all get quite complex, & it may be that the solicitor advised you not to get involved because of that. However, I suspect someone will have to get letters of administration unless the companies holding the assets are willing to pay out without them.
I would suggest you return to the solicitor for further advice.