Ideas on Conducting Voice Recordings

I have had to consider how to conduct Gramps voice recordings for more than one reason; he's deaf, he can be easily confused, and his location isn't as quiet as where i have recorded mum and dads. I have finalised three options: One: Conversation - Simply leave the recording device on the table so Gramp is unaware of the fact he's being recorded, therefor any conversation is completely natural. I would record a conversation between Gramp and my Dad, here I could ask Dad to ask specific questions that would provoke specific answers, or lead to certain stories. I could also record Gramp just mindlessly chatting to passer's by or himself. This would be hard for the audience to follow compared to the conversation option. It would however give a very raw representation of his state of mind. If the audio is hard to follow I don't think there would be a problem, instead the audio could symbolise how detached his mind and  memory are. Just as Tracey Emin used imagery to symbolise parts of her life that lead to her not becoming a dancer in her short film 'Why I never Became a Dancer".
Option two: Writing - Another option would be to write down questions then ask Gramp to answer them vocally (which he would do without any prompt). We quite often use this technique to converse with him as he is so hard of hearing, It also gives him more time to answer, this method would keep him calm throughout the interview, as well as making the audience more able to follow whats going on. The draw back to this idea is that I would want the writing to be filmed, for two reasons; too keep in the same format as mum and dads which are both inspired by Gillian Wearing OBE and Francesca Woodman), also to inform the audience of what Gramp is responding too. Filming the writing in front of Gramp would cause confusion and could lead to the audio becoming more incoherent than neccercary. With me providing the questions the interview would also become more staged than I hope for.
Option three: Plain recording - I could leave a recording device recording in Gramps vicinity for several hours without him knowing, this would be difficult but could produce very interesting results. The problem I could face is that within the hours of recording he doesn't talk about the past, then the voice over to the video wouldn't really link with my theme of memory.