Well, you can get another Sony and that way you guys can trade off lenses. That'll be cheaper in the long haul; but since I have no idea how Sony's DSLRs or lenses are, I can't comment on the quality you'd get.
Sony's DSLRs are pretty good, and their sensor technology (when they do bother to update their bodies) ranges from poor (CMOS sensor models) to outstanding (A55, A580). Their lenses are a bit of a mixed bag, although that's true of *every* manufacturer. Some middling to poor zooms, some excellent pro-level stuff (which the OP is unlikely to buy) and a weird selection of primes which range from niche (135/2.8 STF defocus control, the only AF mirror lens on the market with the 500/8, etc0 to poor to outstanding). Sadly, many of their more affordable primes are plastic body +/- mount these days, although some of these still have very good image quality.
At the risk of repeating myself, every camera manufacturer has pros and cons and good as well as black sheep in its lens lineups.
Pros: full compatibility with every EF lens ever made (since 1980). Some great lenses (85/1.2L, 85/1.8, 70-200/2.8L, 70-200/4L) and widespread availability.
Cons: Some older EF lenses have not been updated for 20+ years and are showing their age on digital bodies.
Nikon: Some great lenses
Cons: Older lenses (AF-D) which require body-driven AF are not compatible with consumer bodies. Tend to be slightly more expensive than Canon/Sony.
Pros: Some great lenses (FA Limited, DA Limited, DA*), very good value for body+lens kits
Cons: Limited lens selection, limited availability.
Olympus/Panasonic Four Thirds
Pros: Some great lenses (150/2, 300/2, 14-35/2, 50/2 Macro, 7-14/4, Leica 25/1.4, Leica 14-150/2.8-3.5)
Cons: Dead system. No fast portrait prime.
Olympus/Panasonic Micro Four Thirds
Pros: very compact system, some great lenses (20/1.7, 7-14/4, 9-18/4-5.6, CV 25/0.95), compatible with nearly all existing lens formats including rangefinder lenses (using adapters).
Cons: Limited selection of native lenses, no fast portrait prime, poor ISO performance compared to the best APS-C DSLRs, limited availability
Pros: Some great lenses, compatibility with old minolta lenses (can be had for very cheap)
Cons: Limited availability, pricing on Zeiss-branded lenses.
All the major manufacturers have niche lenses which are not found in their competitors' lineups, but they are usually not a deciding factor in buying into a system for regular consumers as they are priced out of their reach and tend to be very specialized in use.
Wind, Sand and Stars.