This shouldn't be that difficult....
Mash a little thick in the 5 gal pot with say 3 - 3 /12 gallons strike water for a mash thickness of 1 - 1.16 qt/lb (ref rackers calc http://www.rackers.org/calcs.shtml
) It can be very difficult to mash if the total volume of mash is at the pot limit without spilling the grain all over, so mash intentionally thick to compensate. I would mash in a couple of paint strainer bags, make a bag, or buy a bag, if you desire but not required! This post is meant to be helpful and not a sales pitch, sorry, but just had to say.
After the mash, top up your kettle to the rim with hot water and stir well, and stir well again...or even boiling water if available to raise the temp.
Remove grain bag(s) and sparge / rinse bags in your bucket or 2 gallon pot, even with cold water if that's what you can manage. Using a bag or two will make removing the grain much easier with less mess!
Combine runnings and boil...you can even get 4 gallons boiling and slowly add runnings to max out your small brew kettle so you can finish the boil at say 4.5 gallons.
Top up your fermenter to make your 5 gallon batch...
There is usually a work around when you are under equipped, not a big deal you just need to learn how to "run what you brung" as they say in car racing....cheers!
ps edit...if you want to complicate further, you could boil the batch in both the 5 gallon and the two gallon pot by just distributing the runnings in both pots, and roughly splitting hop additions b/w the pots. This is more like spinning plates but can also be done. Between the two pots you have 7 gallons capacity, you should be able to generate 6+ gallons of wort. I admire your fortitude...cheers and happy brewing!