Solifenacin and tamsulosin are both used to treat peeing multiple times during the night, but for almost opposite reasons, so it seems a bit strange to be on both.
Solifenacin (and tolterodine) are used to treat bladder spasms - these tend to cause you to need to go to the loo before your bladder fills up, so you are only using a part of your bladder capacity, hence needing to go more often.
Tamsulosin is used to treat slow flow, and slow flow can cause failure to empty the bladder because you stop peeing before you had time to empty at a slow flow rate. In this case, you are also only using part of your bladder, but it's the part between half full and completely full, rather than the part between empty and half full.
So the drugs Solifenacin (or tolterodine) and tamsulosin are used in almost opposite scenarios (with the same net symptom of peeing often), and it seems strange to me to be on both of them together.
These are 2 common causes of urinary frequency at night, but it sounds like no one has actually established which (of about 6 possible) causes of night time urinary frequency you have.