Each of your electric items will probably be labeled with how many amps it draws. Figure out about how much time it will run for each day times that devices amps.
So a water pump may draw more amps than say a fantastic fan but it runs only for short periods. Adding up the amps x hours of use for all your electric devices gives you a total number of amp hours you will need per day.
Then take 1/2 the battery capacity in amp hours. Typical deep cycle might be around 100 amp hours, you don't want to draw below 50% charge because that degrades the battery life. So you have (without any charging) about 50 amp hours or 7 amp hours a day. Two batteries would double that.
A 100 watt solar panel
would put back in about 5 amps per hour of good sun. So maybe 4 hrs at 5 amps and 4 when the sun is lower in sky at 2.5 amp output per hour. Total of 30 amp hours a day going back into battery. So if you used 30 amp hours per day your solar
would keep battery charged if you used 37 amp hours per day your battery charge would go down by that 7 amp hours stored power every day.
You don't have to do 100% full charge daily, your solar
(or generator) charging can be used to extend the number of days until your battery gets down to 50% charge even if it doesn't top off the battery every day.
It ends up being a balancing act between draw, and reserve stored in battery and charging and amp hours are the common denominators that allows comparing all on same terms.
I only have two lights
(led) and a fan. Plus whatever phone, tablet, camera etc. I charge. So a 40 watt panel at 1.75 amp hour charge will extend stay on a single battery to longer than dear wife wants to spend in the boondocks.
To be honest I'm pretty sure I could have skipped the solar
, one battery would last as long as she wants to be roughing it. Been there done that, now she likes hot showers close at hand.