If you really need to have separate volume and tone pots for each pickup, you could use the concentric dual pots that Warmoth sells. The advantage of these is that you don't have to drill new holes into your guitar.
The addition of separate volume and tone pots for each pickup will give you pickup output level blending and high-cut tone control, but it WILL NOT effect pitch changes. The tonal changes will only be the variable attenuation of high frequencies. The tone controls in a passive guitar aren't especially profound in their effect.
If the 3-way toggle switch in your guitar doesn't make any tonal differences between pickups selected, it just might be broken or miswired (or just subtle). Based on the normal manufacturer and reseller markups in the industry, if your guitar cost you $200, it was made for about $50 to $60. Don't expect a profound tone machine at this price point.
A real LP is a mahogany body with a maple cap (usually) with a mahogany set neck. These typically street for $800 (faded GC) to $3,000, with $2,000 being the norm for a relatively common one.
A real SG is a mahogany body with a mahogany set neck. These typically street for $600 (faded GC) to $2,400, with $1,500 being the norm for a relatively common one.
These Epi guitars have bolt-on necks with less than premium and less than well-known wood bodies. The pickups won't be especially good either.
These are just the facts, not a comment or reflection on you or your choice. We all started somewhere in our journey. While substantial improvement can be made from effective wiring schemes and pickup replacement, be careful where you do this. If you do make a profound improvement in the sound of this guitar, remember that it will always be what it WAS in lineage, and never will allow you to recoup what you spent on improving it.
For demented wiring schemes, chech out this link: