It's going to be ages for him, at this rate. And no, it doesn't have to be you who guides him. This sounds like a case for a professional nurse who visits daily. There must be some for hire (even at ridiculous rates, perhaps?).

It was months before I could be safely rid of the tube, and my healing mostly went well after the treatment was done. (I had glitches, but they were more surgical issues at that point, or came up much much later.) My treatments ended in March, and I think my signature reminds me the tube came out in June of that year. My whole family worked with me to manage it. I'm not a big eater anyway, which may have helped (my 'normal' isn't super normal, LOL) but I really did need the support to be able to actually eat.

As for syringes, that has baffled me all along. I never had anything like that with my tube. Just a drip bag like for an IV, and I'd have to let gravity do its thing. Could be odd when out in public, but no squirting or forcing more than gravity (which was quite enough, sigh). Is it perhaps going in too fast and upsetting his tummy somehow? But I know they change things quickly in the cancer field, so maybe this is a regional thing, or maybe a new thing.