I think you might be blowing things out of proportion. If you were invited to be hens night and wedding... Then obviously these people like you at least a little bit... Meaning it's possibly not just about a gift grab.
Sounds like you just don't like them to be honest and it might be clouding yor judgement?
If I liked them and enjoyed their company I would buy a cheap baby shower present for them. If I didn't then I would probably lie and say I already had plans that day.