I will say I have slept in a bed with a man, naked no less, on a first date where I was just too tired to worry about getting home and not had sex. I set the boundaries ahead of time and made it clear that I was happy to leave if those were not boundaries that would be respected. And, trust me, I'm no prude. So it can be done. Granted, I did not sleep in the same bed with someone every night for an extended period, but if it is important to someone or a couple then it can be done. I don't understand why, necessarily, one would deny themselves sex with their partner... but I don't know them and if it's important to them, well, whatever. But, as unlikely as it is, it can be done.
Now, as far as the step-grandfather not letting them stay in his house if they are unmarried... I'm of the 'his house, his rules' crowd. I wouldn't let a witness staying in my house have a book study there with a group of witnesses. I find it offensive and shouldn't have to be subjected to what I find to be offensive in my own home that I work hard to pay for. By the same token, this elder is well within his rights to say that he is uncomfortable having unmarried couples stay at his house, even in separate rooms. If he finds it offensive he shouldn't have to be subjected to it in his own home.
Of course, this is all easy for me to say as it's not my daughter, I guess. ;)
Jackie