There are rural counties that will permit you to join 2 homes together, but they have become few and far between, We were permitted to do things like this in the county where I live up to about 5 years ago. I have seen this done a number of times, but not usually successfully.
You need to have someone that has considerable experience in multi-section installations, the ability to adapt that experience to a non-standard situation and the talent to design and fabricate a marriage system that will not sag or leak.. A successful job will most likely require a new pitched roof that spans both units, which can be quiet expensive, considering the price of lumber and roofing materials today.
I purchased a small 24x40 block home. In the late 80s. We attached a 24x44 Fleetwood doublewide to the block home in a "L" shape. We consulted with an engineer, who designed the marriage system and a home builder with 20 years experience to design and frame a new plywood/shingle roof that seamlessly covers the entire home.
We then brought in a plaster contractor who installed stucco siding from the roof line to the ground. The front door side and back of the doublewide was wrapped with a wood deck that the new roof extends over. We spent the next year renovating and modernizing the interior and have lived in the home ever since. The home has stood up against 4 hurricanes here in Florida, in the past 2 years, without incident.
On the other hand I have seen several similar, amateur attempts, that worked well until the first rainy season, when they experienced more damage from settlement and/or rain then that owners could afford to repair.
What you want to do is possible. Talk to the local building authorities to see if this is a permitted consideration where you live. Seek professional guidance and bring in experienced tradesmen. Be prepared to pay top price for these services as you will need the most experienced and talented people available. If you attempt this on your own, or "on the cheep" the odds are that you will be abandoning your home after a very short time.