continuing Stuart's arithmetic, each of you without a railcard would be spending £99.90, with the savings of a Railcard it would reduce to £65.85, saving you £34.05 each or saving £68.10 for the two of you.
Senior Railcards cost £30 each. If you went to the hassle of getting them and remembered to use them each time you would save £8.10. As your first journey is from London to beyond the southeast you would not need to worry about the weekday time restrictions. When your tickets are checked you would need to produce both tickets and both Railcards.
Two Together Railcards cost £30 (but you only need one to cover both of you) plus the cost of photos of each of you if using the plastic card or images if using the app. You would need to ensure your phone had battery or use the plastic card which you would present with the tickets. Two Together Railcards are only valid after 9:30am weekdays or anytime on weekends, and the morning restriction is anywhere in the country. Because you only buy one Railcard your savings is £30 more, less the costs of the photos.
So to me the £8.10 savings on Senior Railcards versus the hassle is probably not worth it - you may feel differently.
The £38.10 (minus photo costs) would buy you a nice lunch, if you can adjust your travel no earlier than 9:30 weekdays.