Method for rechargeable batteries in Parallel
We have to make a few assumptions because I think you forgot to mention some things:


solar panels use a change controller for the appropriate chemistry and voltage
the load is actually an inverter


Sometimes both the charge controller and the inverter is integrated in the same box.

The configuration of the batteries greatly depends on what inverter and charge controler you chose.

12V inverters rarely provide enought power to be very usefull in a house. If you want to be able to use at least 2000W ocasionaly (microwave popcorn while watching TV with some lights on) you'll probably have to go for 24V or 48V for your pack.

I wouldn't mess with saving too much money because if you skimp on using a propper solution you could burn your house down. Get propper electronics and use propper fuses.