Staff nurses and sisters are all RNs, and sister is an older term for a Charge Nurse. Junior and senior sisters roles can vary by specialty, but generally they can both take charge of the shift, and run the clinical area, although the senior sisters tend to have responsibilities beyond the current situation, usually for clinical training, or allocating the 'off-duty' work roster, stock-ordering, liaison with other departments, etc.
That's pretty vague I know, but there is no strict definition, it varies a lot.
Consultant is the senior doc in a specialty. next man down is the registrar, (or sometimes the staff grade), and then the juniors are 'housemen', which is an older term sometimes still used, They are newly quaified, and working their way through clinical placements usually of 6 months duration. They do 2 years intotal, called Foundation Years, and therefore its not uncommon for them to be referred to as FY1s and FY2s.
Just to really confuse you, specialist nurses are sometimes called nurse consultants. Examples would be diabetes specialist nurses, tissue viability/wound care, stoma care, etc. Most have prescribing ability, and are very well paid.
Oh and there are no LPNs, they were called enrolled nurses but have gone now. CNAs are called HCAs, healthcare assistants.
Bet that's all as clear as mud?