How do I not offend people who offer to watch my son?

So I have been told multiple times by multiple people that they would love to watch the baby. I haven't exactly said no more like we will see to so many people because for one they either smoke and the smoke will linger on them and he could breath it in, two I am a stingy mother. He is only two months and I don't see him as much now that I am working and I want him and three I am picky on who watches him. I am very appreciative of the offers but I have my dad watching the baby while I work and we have a good thing going so far. I am constantly updated down to his last poop and if he was read to today. They don't understand that this routine has been great and I don't want it interrupted. I am fine with visits and going to see them but not enough to take care of my baby. It's hard to say we will see. My boyfriend's great grandmother was saying we will need Mawmaw weekends.....no not till he way older... She and my bfs mother and daddy took care of him while I was in the hospital for preeclampsia so they think since they took care of him then that it be easy now lol. Oh no. He is a total different baby. Refuses sleep, eats like a piglet and needs lots interaction as they were use to his fresh newborn self sleeping constantly and that be it. So how do it tell them no without upsetting them? Sorry it is so long been a very stressful day.