Austin isn't a market that would sustain a turnkey company.

I think the house shows a lot better with furniture in it (especially if congruent with photos) but that is an expensive proposition to move everything back in to show it.

Every room has beds, each living room and kitchen has furniture and appliances, and there is also washers and dryers in the basement. 

Sounds like you are confident in the how they obtain their income, if so sustain your current collection process.

which is more sustainable? 

Removed all the outdated furniture, gutted it, new LVP, paint, electrical panel, baseboard heaters, sinks, and remodeled the kitchen with quartz countertops, undermount sink, and subway tile.What was the outcome?

.- They will furnish your unit so in the future if you want to do the STR yourself, you can purchase the furniture from them, you will have data that it works, etc

The long term outlook on the fundamentals cannot sustain this insane market. 

If you go that route, a little hack I always recommend is using an airline miles/hotel points CC to purchase all of the furniture and then pay off the card...might as well get as many benefits as you can.Finally as a friendly reminder, you don't need 100 doors like others to be happy to make some side cash flow.

If the company makes money and can sustain new purchases from the profit or if all 3 of you are ready to split the investment on new properties i would change the split to 33.3% for each one and maybe call your brother in for some work.