What is the best way to help a heavy person up from the ground?

A physical therapist consult is in order; ask your husband's MD for one. THAT SAID there is NO way that you can get up a person without injury alone. You should call the Fire Department and ask if they have an emergency lift team. You should ask the doctor if he knows of one. Enlisting the help of neighbors leaves them open to injury as they attempt to help, and you and your husband open to lawsuit.
You may know that you are facing a coming time when you cannot do this alone. I am so sorry, but an injury to you will put you out of commission. I am stuck life long with the "Old Nurse's Back". There is really no way to move even smaller people, over time, without sustaining an injury. I don't know a single nurse without the "back thing". You can't afford that. Your husband, wherever he has to live, needs you whole and there for him. I am so sorry. Wish I had more for you.

i have a single blow up bed that gets up to chair height once blown up. Slide the deflated bed under your parent. Plug up pump and turn it on. Hold them steady while it inflates. Once its full they should be able to swing their legs over the side and you can help them stand.

Do not lift him.

If there's no Falls Response or similar service near you, have a look online and you will see the kind of equipment used to lift patients safely. It is not prohibitively expensive, but you would be foolish to buy one and use it without at least asking an occupational therapist or physical therapist to show you how to do it properly.

911 for a non emergency lift assist.. In my area there is no charge for this and they have never been condescending or sarcastic. Very helpful, friendly and competent people.
However, it will get your neighbors attention if the bring the high lift ladder truck that takes two drivers plus an ambulance.
I enjoy the looks of the gawking neighbors faces myself.

Unless the house is on fire, DO NOT, under any circumstances, try to get him up by yourself, no matter how much he yells and demands that you help him up.

I know a lady who tried to help her husband out of the bed and he fell, pulling her down with him, severely injuring her back.

He needs some good, regular PT and also needs to be using a rollater or walker.

Here were I live (Florida) there is a service called LIFT. They come to your house and Lift the person off the floor and the assess whether or not that person needs to go to Hospital. No charge.

My 94yr old mother fell in her bathroom. She was not hurt. She could not get up by herself this time. She has very bad knees. Usually she grabs the sink (with vanity) and pulls herself up. I have back issues so I was no good to her at that point. She scooted herself into her bedroom and tried to climb onto her bed, which had been lowered about 6” for safety. That did not work either. We tried her cedar chest. That also didn’t work. After trying for about 45minutes she was exhausted. She was adamant she was NOT going to call for help! Then I had an idea. If I could get her out of her room, down the long hallway, thru the foyer to the 2 steps down to the family room, she could use the hand rails and pull herself up.
So. I went to the garage, got the furniture dolly, wheeled it into her. She looked at it and said “OH NO” She was sitting, so I slid the dolly as close to her backside as I could get and she wiggled onto it. I leaned her backwards and off we went!! At this point we were laughing so hard and stating how proud Dad would be if he were here to see her being wheeled thru the house on a dolly! We got to the steps, I lowered the dolly, her feet were on the first step going down, she grabbed the handrail, I helped her to stand up, and she stood right up. That was a year ago. I haven’t had to use it again, but we still giggle about it. A 94 yr old woman sitting on a dolly being pushed thru the house by her 69 yr old daughter. That may not work for everyone, but it worked for us that night. Ah. The memories.

I knew a family member who once called the fire department after the patient fell to the floor. He was over six feet and too heavy to lift. The firemen were glad to help. That is what I would do.
I lifted a 5 gal bottle once and hurt my back. Take care of your back, pain can be excruciating. I did not use good body mechanics. We use a Hoyer lift when my mother has a bad day, although it is rare, it is safer for both of us.

I have called the fire department, they come, put him in bed, he refuses transport to hospital, all is well. However, I also bought but have yet to use, two twin size inflatable Intex air matts. My thinking is, if I can put them both under him, he can just lay flat on them,inflate, they will raise him almost 3 feet off the ground. Then he can sit up, put his feet on the floor,and grab his walker, then stand. As I say, I have not tried this yet as thus far the firemen have come and been very nice, not had any threats or arguments over taking him.

I am 78, have two bad knees but some arm strength. I often have helped get my neighbors up off the floor in the elderly home where we live. They don't want to call for help because help people often insist on taking them to the hospital. I found a way to help them up myself. I get a medium weight chair with wooden arms (we have a lot of these around). I get the person on their knees facing the seat of the chair and tell them to grab onto arms of the chair. Then I get behind them and put my arms around their waist. Now I am not going to lift them, this is just to stabilize them and hopefully keep them from dropping back down. If you can get a pillow under or in front of the knees this helps but there is no need to put all their weight on their knees. They need to lean on their arms on the chair seat or chair arms. Then they need to shift their weight forward, leaning into the chair. This is an important step. They should not remain in a straight posture. You tell them to put one foot flat on the floor or as flat as possible and push up while you assist the forward and upward movement. This is actually not lifting but pushing them into the forward motion. Also giving them the feeling of support because I have found some people are afraid of falling back. It is important to have them shift their weight forward into the chair. I have shown some people how to do this by themselves if they are home alone and some can do it. Of course this is for people who can follow instructions. You might try practising this with someone not disabled first. Also I find if someone has just fallen it can be good to let them sit there fir a few minutes to get their bearings first because it can be a bit of a shock.