You are doubling your transaction side exposure, adding far stricter license law regulations, stricter accounting regulations, billing & bidding approval processes & much much more.By all means give it a go but the age old phrase you don't know what you don't know looks like it's going to bite you in the butt here.

With the age of the property (1820s) you should definitely be more conservative.  

The real potential problem with a mastiff of that age is not the injury it could cause to a person, but to the damage it could do to the property.They do loose bladder function as they age, and they have a large bladder. 

That might mean you could dispose of the property in total only after that gifted element has aged sufficiently to get 121 benefits for the entire sale price.

They have four or five children ages from 2 to 7.

You and your Solo 401(k) are distinct taxpayers in the eyes of the IRS,Trump tax reform has precluded the "netting" of income/loss from separate business activities that are subject to UBIT.If your objective relates to #3 (above), there would be benefit derived from a cost seg study - assuming the Mobile Home Park investment is truly subject to UBIT.    

We are all taught from an early age to go out there and get money, to make as much money as possible and that once we are at that very high level of lots of money ONLY THEN can we really be happy. 

I would second @Tom S. and consider house hacking a small multi at your age. 

Managing a lot of single-family rentals is different when you are in your 30s than when closing on retirement age, so you can always sale your appreciated portfolio and deploy that capital into a more passive play or start doing that when you think it's appropriate for you.Good luck 👍🏾👍🏾👍🏾 

The age of the notes means I wasn't worried about previous liens, and jr liens would be cleared by the foreclosure.