It does sound like a tricky situation. Have you tried explaining exactly why you want to take things slowly? Maybe if you point out what makes you think the hamster is uncomfortable (flinching, shying away, avoiding contact..), your family member will also realise the pace they're going at is too fast.
Also I'd try taming the hamster together, there is no need to cut the family member out or anything as I'm sure they're just trying to be helpful. To be honest it's quite nice they have an interest in hamsters, a lot of people don't! If you get a large playpen to sit in you can take it in turns with feeding treats and handling, and can probably even offer them advice if needed.
There are some taming steps too. Like
this one on the wiki - if you've decided to follow similar steps it does show you've thought it all out instead of just seemingly not knowing how to progress. Might help if your family member thinks they know everything!
Even if it does continue and the taming ends up progressing more slowly, hamsters do know the difference between who handles them, they can sense your energy. So I've had some rather nippy hamsters before who took a lot of time to stop that habit, but even after they stopped they still only tolerated me handling them without nipping. So I don't think it'll necessarily have too much of an effect on your own bond with the hamster.