Hi Paul as a rule of thumb a 110AH battery would probably be better for running two pumps, However as you are only looking to do this two days a week it may be ok.
There are a number of factors which will impact on battery use. A pump will draw between 3 and 8 amps an hours depending on whether you use a controller and what flow rates you run the pump at, Two pumps then will draw 6 - 16 amps an hour.
Battery manufacturers suggest you should not deplete a leisure battery below 50% of capacity in amps terms or 10.5V dropping the battery below this level on a regular basis will cause damage to the battery cells.
So if you start with a full battery at 75 amps every day you have 37.5 amps of usable current. Your split relay will only put back in some of the amps you use each day and how much goes back in will depend on how much driving you do during the day.
I would suggest bench charging the battery before and after you have run two pumps from it.
https://www.linkedin.com/pulse/12v-deep-cycle-batteries-ian-sheppard?trk=hp-feed-article-titlegoes into a little more detail