I find this whole area fascinating. Can what happened to previous generations eg. our parents and grandparents be causing us physical and mental issues now, not just from a learned behaviour point of view, but from a genetic methylation changes stance?

The research is suggesting it can. An overview on this you might find useful is here:

The Impact of Trauma on Future Generations

The most interesting bit for me is that they found the methylation on affected genes have been downgraded, not upregulated in offspring In other words, the next generations had effectively created trauma resistance, as I see it: an adaptive response. I note that the researchers measured cortisol response – I wonder if that means the stress response (high cortisol) in the survivors and adrenal fatigue (low cortisol) in the offspring.

Here’s the original study abstract so you can have a read. I look forward to more research on this.