For highest image quality the two prime lenses beat the zoom.
Here's a side by side comparison of the Tamron 24-70 set at 50mm and f/2.8 with the Sigma 50mm f/1.4 Art set at f/2.8. Both are Canon versions of the lens mounted on an EOS 1Ds Mark III which is a 21MP Full Frame camera. The 50mm prime is noticeably sharper at all common apertures, especially in the mid frames and corners, but also in the center. The 50mm prime at f/2.0 is about the same as the 24-70 at f/2.8 in terms of sharpness!
And here is the same comparison between the Tamron 24-70 and the Sigma 35mm f/1.4 Art. The difference in the center of the frame is much more subtle as the Tamron does a little better in the center at 35mm than it did at 50mm, but the differences in the mid-frame and corners is still quite significant.
And here's a comprehensive comparison between the Tamron 24-70mm f/2.8 Di VC and the Sigma GLobal Vision 35mm f/1.4 Art. (Ignore the "Scores" tab, which evaluates the zoom over its entire focal length range and weights the various factors of lens performance in a way you might or might not weight them. Instead, to view the actual measurement data, click on the "Measurements" tab, then Sharpness-->Profiles and the appropriate aperture and focal length selections. You can also view the tabs for distortion, vignetting, and CA.) Both are tested on the Nikon D750. Tests of the newer 50mm f/1.4 Art have not yet been released by DxO Mark. In addition to the superior sharpness of the 35mm lens, the prime also demonstrates less vignetting at f/1.8 and substantially less at f/2.8 than the zoom does at f/2.8. The 35mm prime also demonstrates much less chromatic aberration across the entire aperture range than the Tamron does at any aperture.
For maximum coverage of most scenarios, the zoom beats the two primes.
With the zoom you get coverage from the edge of wide angle at 24mm to the edge of telephoto at 70mm and all of the normal range in between. And you get that coverage without needing to change lenses every time you wish to change focal lengths. In very low light, the additional two stops of the f/1.4 aperture provided by both the prime lenses may allow you to get a shot the f/2.8 zoom wouldn't, but you must also be mindful that at f/1.4 the depth of field is very shallow and might also prevent you from getting everything you wish into focus within that narrow depth of field.
You have to decide which outweighs the other for you.