How to Synchronize two RTC module one internal and other external

It could be a SCART switching issue. With SCART, some TVs need a low signal on pin 16 to select RGB rather than composite.

http://freespace.virgin.net/matt.waite/resource/av/scart.htm#Note%202%20:

You could also try putting your composite signal into one of the RGB channels to see if it's picked up properly.

I believe your calculations are mixing frequency and time periods.

1 / 125000 Hz equals a period of 8 us. FOSC/4 divides the frequency further down (or multiplies the period). You cannot multiply a frequency without special circuitry. The prescaler also divides the frequency, or multiples the period. So instead of dividing the 8 us by 4*2, you need to multiply it by 8: 8 * 4 * 2 = a period of 64 us, or 64 times what you thought it was.

Unfortunately, 1000 doesn't divide evenly by 64, so you can't get a exact 1 ms interrupt. Instead you should probably use a clock frequency of 1 MHz (OSCCON = 0b01000000) for a period of 1 us. Then 8 * 1 us equals 8 us, and you can use a clock preset of 256-125=134 or 0x86 and get an interrupt every 1 ms. Count every 100 of those for your 100 ms timing.

As an alternative, if power consumption is an issue, you could set the clock frequency to 250 KHz (just double what you were using), and get an interrupt every 4 ms. Then count 25 of those for 100 ms timing.