Sounds like overstimulation to me. I had very similar problems with my DD.

The good news is that, as I understand it, most babies sort it out by about 3 months. So it won't last forever.

In the meantime, you either have to just put up with it, or be firmer about people not overdoing it with the baby. I found it difficult to do the latter, but by the time I got really exhausted because she was impossible to settle at night, I was much more motivated to tell my mum to take it easy.

One option is to put baby in a sling and carry her yourself while they are there. If she's sleeping, then they will understand it's not OK to disturb her. And even if she isn't, explain to them that she's having a rough day and needs her mum.

Don't forget: it will probably get better quite soon, once your baby learns how to switch her attention off so she doesn't get overstimulated (my DD did this by breaking eye contact with people who looked at her and gazing at the ceiling instead). So you won't have to deal with this issue forwever.