I'm not going to address the "should you have a gate" or not, because it's not relevant here.
When you're a grandparent, one of the hardest things you will do is to recognize that your relationship has changed. You're not in loco parentis any more, assuming your child is an adult and on their own. There's a huge difference between offering advice and substituting your judgement for theirs; from the language of the question, you haven't mastered that difference yet. One hint as to mastering that: if you have offered the same advice more than once, it's no longer offering advice.
It's important to recognize that you cannot subsitute your judgement for theirs. What that means is, when they evaluate the risks and benefits of a particular course of action, you must not tell them that they're wrong just because you disagree. Doing that harms your relationship significantly, and can harm your child as well. Either they get tired of you telling them what to do and stop coming to see you/letting you come over, or you devastate their self esteem as they think you don't believe they're capable of parenting safely.
As a parent, it's great to get advice from others as to what to look out for, what the dangers are and the risks. Sometimes you don't recognize every risk, and it's very helpful to have those pointed out. But recognize that as a grandparent, you're not going to evaluate the risks the same even as you did as a parent. You're not there with the kids 24/7; you don't see them and see everything they do. Further, as you age you become more risk averse; i.e., you are more concerned about risk than you were as a parent!
I'll end with my experience here. Our relationship with our childrens' grandparents is relatively good, but it definitely was a bit complicated to get there. It took a while to go through the "you're not feeding your children enough," "you're letting them go outside without a coat when it's cold," and "you're taking them to a busy museum and not holding their hand the whole time?" phase. Eventually, they learned that we were good parents who knew how to manage risk - and we tolerate the occasional bit of advice, even though sometimes it's really just second guessing. You will find this spot for yourself - but you'll find it faster, and easier, if you start from the assumption your child is a competent adult who can make their own choices.
If I insist now, my daughter will feel guilty... If I don't insist now, then I shall feel guiltywhat if the fence is installed, but it results non-sufficient i.e. the granddaughter sleepwalks, climbs the fence and falls from the stairs? who would fell guilty then? – Josh Part Apr 25 '22 at 15:10Meanwhile did you notice which part of "15–30% of kids sleepwalk at least once" mattered?
If 15–30% of kids had a sleep-walking habit, that might be tragic.
If all kids sleepwalk at least once, is that really likely to be problem?
I have a larger family than many, and in the last 100 years we've heard of one girl sleepwalking, once.
– Robbie Goodwin Apr 27 '22 at 18:49