The best way to connect them is too know the batteries conditions.
Charge them and measure their gravity and if close to each other with the same voltage (within 2%) when left standing without any load after 4 or so hours, then you may parallel them directly, though I would have the paralleling in a way to separate them easily for periodic testing.
We have paralleled banks without ill effect for long periods of time, one needs to understand the intransigent behavior of the batteries, their voltage and their internal resistance.
The diodes you want to use for isolation do have a lot of un-necessary losses during charging and discharging and if you examine the connection you wil see that the diodes will do one thing, spend power and keep the batteries at the same voltage, which will be the same with or without diodes.
Nando