I do not think you are going to be able to modulate your 205Hz pwm output with 20/40/50Hz sine waves with any reasonable resolution because the output frequency is too low and the sine wave frequencies are too close.
You can only output 205 values per second. Most sine wave digitization is at least 8 bits with a lookup table of 256 values. For an 8 bit representation of 20Hz sine wave you need to output 20x256 = 5120 values in a second. Clearly at 205Hz you can not get to all the values in the table in one second and can only output 205 of the 5120. At 40Hz and 50Hz you sample even less of the values required (40x256 =10240 or 50x256= 12800)in a second.
I believe that this undersampling can be handled with DDS (direct digital synthesis) techniques KO7M - Ham Radio Blog: Direct Digital Synthesis (DDS)
but this is fairly complex. I think, for example, that with the case of 205Hz trying to get through 5120 samples you ouput every 20th value in the sine table and step through with different starting points each pass. Whether or not synthesizing a complete sine wave with this proceedure is useful for an LRA and its driver is unknown.
If you try to digitize the sine wave with a resolution suitable for the 205Hz there is very poor resolution.
I don't know your application, but there is a different driver (DRV2605) with multiple built in drive waveforms for different haptic effect. You might want to think about getting one of these modules which has that chip.Overview | Adafruit DRV2605L Haptic Controller Breakout | Adafruit Learning System