The way these stories go, gramps will now live longer life because Dylan gave him medicine(al) herbs and told him to check in with his doctor more often, right? lol. I can't wait for Adeline to show up. Just hoping we're not doing the heroine reversal trope.
@AnimefangirlX Agree, the idea by itself is kinda creepy. However, in this particular story I think they did a lot to make it a lot less creepy -- he already notes how she's different from his old crush, which already tells you he knows she's not his old crush and his grandson is not himself. A huge part of it is, he doesn't really judge if it's good or bad that she's not a dead ringer for his dead woman -- Dylan's just a different girl from his old crush and he isn't disappointed that they aren't both into the same types of flowers. When he does make a judgement on her traits, it's usually framed in terms of being good for his grandson, not for himself -- at one point he says her personality isn't quite like her grandmother's/his crush but is more like his grandsons, and he thinks this makes them a good match with each other, not with himself or his dead crush.
It'd be a different story if the couple were a mismatch and he still insisted on marrying them. Or, if he was as hung up on his old dead woman as you say, then what should happen is he would insist on Emily instead of Dylan, because Emily looks more like her grandmother/his old crush (if what the girls themselves want don't matter to him, then their personalities shouldn't matter to him either. Personality/desire both would be an expression of how each individual girl is different from his old crush after all).
Instead, you get a grandpa who thinks he's meeting someone who already agreed to marry his grandson (he doesn't know she agreed under stress), who was already dumped by her ex in favour of her sister (so it's a plus point that he properly looks at her and lists off her many positive traits), directly assesses several parts of her personality that he thinks matches his grandson (he really does think they're a couple), and then compliments her on being a great match while not knowing she wants to break it off -- nowhere in the conversation does he ever get the chance to realise she doesn't want the marriage to go ahead. It just looks a lot more wholesome since he's already acknowledge she's not the same person as his old crush and he seems to think she has a great personality on her own.
If you want my opinion, the whole thing is definitely just a deus ex machina to get some mighty rich city aristocrat to go out and pick up the country girl aristocrat so that hilarity can ensue. But if you want an in-universe excuse, you should also consider that ML doesn't seem to be a recluse and still managed not to form any attachments to the girls who are already around him, so gramps may have pushed for this engagement because the heir probably has to get married and pop out next heirs at some point and this heir didn't seem to be getting anywhere with it. It's not like gramps broke up a couple to get his desired pairing, he pushed a little bit, and apparently a girl that suits his grandson fell out of the bushes and agreed to marry his grandson, so everything worked out (to him, anyway).