For a family railcard you absolutely NEED a child (max age 15) travelling with you - not just a child's ticket. If the child is not with you you will have to pay for entirely new tickets and possibly a penalty fare. You can 'borrow' a child, and it doesn't have to be the same one each time, but s/he MUST be with you
For a senior railcard you have to be 60, not 55.
You could get a Network railcard - this is valid in London and the South East only though on some routes stretches remarkably far
A few companies have sporadic offers (club55) for the over 55s. Any prof of age will do
In the Midlands there's a Two Together railcard - you would be eligible for one if you live in certain postcode areas. Travel can be nationwide
Note that none of these are 'passes' which give free travel. They are railcards that give discounted travel