Maybe it's useful to look at some of the broader issues.
There's a lot of parents whose children have tantrums and a lot of articles about the subject. A lot of the articles seem to focus on children between 2 and 4 who experience this kind of emotional meltdown.
The OP's child is younger 19 months. So some of the techniques that may be appropriate to a child who is twice that age, may not help - or may even hinder - someone who isn't 2 yet.
Then there's the background stuff. It sounds like the child's father is in hospital and is not at all well. If the child had been used to living with their Dad and/or seeing them lots, then the child is going to be distressed by their father's absence/disappearance. They won't understand much about illness or hospitals or getting better. It's all very scary.
The poster has said that she is experiencing depression. It's not clear what help she is getting from the NHS for this. But it sounds like her own mother is not able to help at all, and is positively hindering matters. Plus of course her partner is ill. It'svery tough trying to take sole care of a child, when nobody is taking proper care of you.
It is quite possible that the child senses his mother is unhappy, his Dad has gone off somewhere and that his grandmother is not being loving towards him. In these circumstances it's not surprising that he's sad and angry.
So maybe it's not just about the immediate strategies of dealing with tantrums, but also about trying to access support for the whole family - which may help to make a child feel happier and more secure - so the meltdowns are less severe and less frequent.