If an object is set to be a tint of a CMYK color, the result is the same as multiplying the "solid" values by the tint. E.g., a 50% tint of 100/0/80/10 is exactly the same as a 100% tint of 50/0/40/5. There is no difference in the output. The only distinction is that within Indesign, you can instantly change all of the tints by changing the parent color when you use tints instead of solids.
So you could give them the CMYK values of the primary colors, along with the tint percentages, and let them figure it out, or you could do the math on each one yourself. A quicker and slightly less precise way to get the final values of each color would be to turn on separations preview (Shift-F6 to make the palette appear), and hover the cursor over every color to see the final CMYK values. This is less precise because it will round to the nearest whole percentage.
The "hex codes" are a way of encoding RGB colors (not CMYK) in HTML. Since HTML is almost exclusively used to display images on monitors, the colors are always RGB, and will appear differently on different monitors (at least for Windows computers, which are by far the largest share). If they want the best match for the average viewer, they should not take the RGB values of the primary CMYK colors and "tint" them back to match the CMYK tints.
To get the best RGB values for the average viewer, I suggest the following:
1) Create a page in Indesign with all of your colors on it and export it as a PDF.
2) Open the PDF in Photoshop, choosing CMYK as the color mode.
3) Use the info palette in Photoshop to check and verify the CMYK values of the swatches.
4) Use Edit>Assign Profile... to assign a CMYK profile that best represents your most common output condition (choose "U.S. Web Coated SWOP v2" if you don't know or don't have such a profile)
5) Use Edit>Convert to Profile... to convert to the "sRGB IEC..." profile (use Adobe engine, Relative Colorimetric intent, Black Point Compensation, but NO dither)
6) Save this document and give it to the web people - they should be able to sample the RGB values and derive their hex codes. If you want to show off and give them those yourself, click on one of the eye dropper icons in the info palette and change it to "Web color." The hex codes for each color are just a concatenation of the two digit codes for R,G and B. So if you have 0A for red, E9 for green, and 15 for blue, the code is 0AE915.
