Mcu datasheet from microchip's website
pic16f1825: **broken link removed**
On page 4, you will se a table of the mcu pin functions.
Not sure if you are aware yet that i2c makes use of 2 wires(and that those 2 lines are called sda and scl)
Sda - data line
Scl - clock
You are probably going to be using the pdip package (14 pins). According to the table, SDA is pin 9 of the device while SCL is pin 10.
You connect these pins to the sda and scl pins of your sensors. A very important thing about i2c is you will need pull up resistors on both scl and sda. So connect these lines to vdd via resistors. You only need 1 resistor for scl and 1 for sda so there is no need to add pull up resistors per i2c on each device. I hope this makes sense.
Aside from power and sensor connections, are you also aware of the minimum hardware requirements for the pic mcu? Your basic mcu circuit without sensors should look like this:
http://picpgm.picprojects.net/hardware/picpgm_lvisp_connect2target.png
Edit: just saw your new post and thought i'd add a few more things.
I don't think you need to worry about the exact values of the pullups for now, but id say 10k should work fine. I2c is actually a data bus, and it was designed so multiple device could communicate using these 2 lines only.