Thoughts on this - am I overthinking

So I have a toddler son. Who my mum his grandma takes him out every so often with her friends. I’ve met them about 4 times in person. Since he’s become a toddler they always ask my mum if they can take him out all together even wanting to take him to lap land for 4 nights. I find it strange that they wanna spend so much time with him with me being there. If they don’t like me I don’t get why they think I would let them have my son so often or at all. I don’t trust my mum with him because of things that have happened in the past and she overrides my decision with my son with most things and who he spends time with. Unfortunately I have to work and I’m trying to cut the cost of nursery fees so he now stays with her one day a week. There’s a couple people my mum takes my son around who have nothing nice to say about me & talking to my son about going to town again and I was shocked because I didn’t know and I told my mum don’t take my son to their house again we not been friends for years and her and her husband are quite disrespectful toward me because my mum asked me to be her bridesmaid and I declined - seeing as we hadn’t spoken in years and the friendship was one sided as soon as I stopped making effort never heard from her again. I don’t want to argue with my mum overstepping my boundaries again as she says she understands then goes and does what she wants. I don’t understand people wanting to be around my son knowing that they don’t particularly like his mother. I just find it really strange. Is this normal am I overthinking it? I don’t trust a lot of people and I do worry about my son a lot of especially when he’s in my mums care.