Scanned copy of Sponsorship letter and bank statement OK?

[hrv1983]

• We are a family of 5. Father in law (71 age)
  Mother in law (65), myself, husband and baby 1 year old.
  My in laws stay in delhi and we are in Bangalore. We are planning to visit in march end to Uk for 15 days.
  
  My queries are
  1) what document exactly do we give for income tax return [ form 16 or Itr V or email from cpc]
  2) husband has salary account that doesn't have my name. I need to give my seperate band statement ? I am dependant on husband.
  3) any special document for baby required ?
  4) my passport has my name before marriage. My marriage certificate has my name with husband surname. Should that be any issue ?
  5) what should be the minimum fund to be shown for 5people. I have my savings before marriage, can I show that too ?
  6) do senior citizen get visa easily
  7) we have a relative staying in UK. Should we take an invite letter from them that we shall be stayin with them.

[hrv1983]

IS it ok if the sponsorer isn't ready to share their bank statement ?
Only the sponsor letter & declaration of their income is fine ? They are UK citizen.