In post #4 you say that there are lots of misspelled/alternate spelling of name/address in both Table One and Table Two I suggest that you first identify records with spelling mistakes and correct them, then where there are alternate spellings, choose one.
Group - GroupMembership - Member - MemberAdress - Address
Group: Records details about each group
Member: Records details about members
GroupMembership: Two foreign key fields, one with group id and one with member id
Address: Records a single address
MemberAddress: Two foreign key fields, one with member id and one with address id
Is the combination of first name and last name what you will be using to identify duplicate user entities? The obvious problem with this approach is that two people with the same first and last name will be combined into a single person. Not ideal but is this something you’re willing to except considering there isn’t really any other way to differentiate separate users with the same first and last name? You could maybe lag and isolate users with the same first name and last that appear more then x times in the table. For example, if John Smith appears 10 times its most likely the case there are separate users with the same name?