Hm, 7 and 8 is not at all that old for a small shih tzu. I mean, yes they're old but not to the point of urinating in the house bc of it. I would say it has more to do with routine and the fact that your stuff is ready to move and they are confused. They are probably marking it to remind them (and others) that THEY live there. My dog has been through 4 or 5 moves in his time and each time we had to take him more frequently outside and he peed inside too. It was frustrating but understand how unnerving all this s for a dog. Everything they have is being shifted. Strange people coming into their house, while their not there, may be upsetting. The smells and sounds of a move. The tension from you as you get more and more frustrated.
Trust me here, try a male wrap. Coco has one, he knows how cool they are. they're called Male Restrictive Bands. I use it for Coco's peeing while we're gone. Check a dog store, I found only a couple large chain stores carried them. I was lucky to get mine on sale too

I buy regular old maxi pads and voila! When he pees he pees on himself (not very sanitary I know) and when we come home we just towel him off -not very often though bc its not that bad- and let him outside in the back. He relieves himself and then proceeds to clean himself :/ Anyway, I'll get you a link from amazon and you can get an idea.
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias=aps&field-keywords=male+dog+bands&x=0&y=0