DS1 was 6 weeks prem and was started on home puréed food for the first few weeks of weaning. I gave him a spoon so he could learn to feed himself, while I had a spoon and gave him a few mouthfuls to make sure at least some got in!
He didn't enjoy lumpy food at first but I gradually increased lumpiness by mashing it less each time. From 6mo his food was basically whatever I made for us minus the salt - I did a lot of batch cooking of meals like fish pie, lasagne, pasta dishes, cottage pie, etc, and froze extra portions as meals for him.
From about 8mo his meals were a mix of mashed and finger foods. The finger foods got played with a fair bit at first but he soon got better at feeding himself, and liked having a piece of toast or whatever in one hand, and his spoon in the other.
He was quite ill at 10mo and as a result lost a lot of weight, so the dietician advised us to add cream to things like porridge or mashed potato, and feed him high calorie foods (avocado etc), to try and get his weight up. He loved cheese sauce so I'd put a dollop of that on his veg too.
If your parents are reluctant to let him feed himself because of the mess, I recommend investing in a large drop cloth/oil cloth to put down so it will catch the vast majority of the mess. I got one that I could just bung in the washer afterwards. I also recommend eating meals together so he can watch how you use a fork/spoon and he will learn from you. Yes it's a bit daffy, and your dinner will often go cold while you help him, but it won't be forever. 2yo DS2 is so good at self feeding, his is often gone by the time I sit down to eat (then he's after half of mine!)
It's hard when you're working, but I found that batch cooking and freezing portions made life so much easier as I always had a stock of meals ready to go, and I saved a fortune too.