I have seen two bridge rectifiers instead of one, to increase the capacity on a single phase application, and each rectifier had the two AC connections joined to each other. It is a good idea to arrange the rectifiers like that so that you don't get a thermal imbalance between different bridge rectifiers. If that single-phase application had connected each AC line to both bridge rectifiers, there would have been the risk that one bridge rectifier took more current, so got hotter, resulting in a lower voltage drop, taking even more of the current, and so on.
Joining the two AC inputs will reduce the voltage drop and will increase the capacity, but it will be nowhere near a doubling of the capacity. If you look at the voltage - current curves for the rectifiers, such as here
https://www.farnell.com/datasheets/2864019.pdf on figure 3, you will see that the voltage across the diode will only be reduced by a small amount, maybe 10%, so there will still be 90% as much heat to dissipate.
I don't think that you need current sharing resistors to share the current within a single bridge rectifier, as there is very good thermal connection between the diodes anyhow. Also, the circuit has worked fine with 100% of the current being taken by one diode, at a time, so if you get an imperfect split of current, say 75% - 25%, it's only a slight improvement but it is still an improvement. Current sharing resistors would generate more heat than the reduction you would get by using both AC connections.