Hi @Bluesky5512 I would find those touches (very) uncomfortable too. I can see why he has probably changed since his wife's death, and now wants/needs more physical contact, but there is no-way you should have to put up with them. I think that his Son needs to have some discussions with his Dad, and gently explain to him that although you love him, and the conversations that you have with him, you are not a very tactile person, so could he please stop touching you.
I think that if he then does it again it will be much easier for you to move slightly away from him, and say something along the lines of "I thought Dave told you Dad that I don't like being touched, so please try not to. It doesn't mean that I don't love or care for you, it is just that in my family we were not very tactile".
Apart from an initial hug and a kiss on the cheek when I see someone I care about, I absolutely hate being touched by, or having my personal space taken up by, most other people. There are only 9 people who I love giving hugs to, and having cuddles from, and 3 of them are my Grandchildren! The others are my Husband, my Children and their long-term partners (I am very lucky that they have absolutely wonderful partners, who I love very much).
Unfortunately for me, only my first born is at all a tactile person, so I never try to hug any of the others apart from my youngest Grandchildren who are still babies. But as soon as they show that they don't want hugging or kissing anymore, I will stop. I don't agree with making children give grandma, or auntie or anyone really, a hug and/or a kiss, if they don't want to.
My oldest Granddaughter has not been keen on being hugged or kissed since she was about 2.5 years old, and when her Mum used to tell her to give her Grandma or Granddad (us) a kiss goodbye when she very obviously didn't want to, I would ask her Mum to not force her to, but I would also laugh and tell my DGD how much I loved her, and then blow her a kiss, which she would then often bat away with her hand - but we would grin at each other as she did it!
I think that the PPs on here who wouldn't mind having their cheeks pinched, or having hands put on their shoulders (which is often a way of restraining people and having control over them), or even an arm around their waist, by anyone who isn't their partner or a young family member, are the strange ones. I really do think that his behaviour needs nipping in the bud sooner rather than later - which has probably already happened by now as my one finger tying on my phone takes me so long! If it hasn't been sorted yet OP then I am wishing you lots of luck in getting things back on an even keel very soon. 💐💐💐