Reading from multiple sensors and synchronizing data
Why not use ONE micro with FOUR ADC's (not a hard thing to find) that reads all four values at once, then reports the data back over ONE serial link?

Without more detail about your setup I suspect you're deluding yourself about your ability to get 1mS accuracy/synchronisation too.

Edited to add: If you can give more detail about the application there are lots of other solutions; 1ksps is easily doable through the laptop sound-card (most will do 96kHz/16-bit on 2-channels, many can manage better / more channels).

Edit now we have more info:

Sensor 1: Quadrature encoder = 3 GPIO pins (as A,B,I are just logic levels)

Sensor 2: Lazer = 1 UART

Sensor 3: accelerometer = 4x ADC's

Sensor 4: inclinometer = Another UART

Connection to base: = Another UART

So that's 3 GPIO, 4 ADC and 3 UART - which is doable with ONE of your current PIC devcies, if you're willing to bit-bang an extra UART port (plenty of PIC bit-bang UART routines on the google). It would be easier using a single chip that has a spare UART or some other port, but perhaps your inclinometer or laser could use SPI/I2C? Just a thought.

I'd question your specification for the synchronisation of any of this (given the sample->conversion->UART->PIC->UART path for the Laser &amp; Inclinometer), it seems to me everything will be subject to different amounts of delay, even if the data is reported back in one hit every 1mS it's likely to be out-of-sync with itself by some degree.