Can I remove a chimney breast in bedroom without affecting the chimney and fire in the ground floor?

Yes it is but you’ll have to run the flue from the downstairs fire externally which might be possible if you’re house is detached using twin walled insulated flue or a fan assisted balanced glued appliance. If you’re removing a chimney breast remember to support what’s left above also with gallow brackets and a concrete lintel or the chimney stack will be unsafe. You could take the whole stack out and do a little roofing. Lots of options tbh.

You can but it means supporting the chimney in the loft and replacing the flue for downstairs fireplace with factory made insulated pipework . Then this must be boxed in using non combustible materials And connected in between floors .

No you won’t be able to use your chimney once you have taken the upstairs breast away , you can only use the chimney downstairs as a feature