What if some of the symbols in a cross stitch pattern are the same?

As for the two symbols standing for two things, I've never seen that before. I'd take a close look at the image in color (probably came on the package so you could see what you're buying, or you can search online) and see if you can tell. If not, go with whatever makes the most sense. Remember, you aren't displaying this with a copy of the pattern next to it, no one will know but you (and maybe your sister). Also, tweeding is really easy, so I'd pay attention to the asterisks; often the two colors that are used in tweeding together will have a separate symbol.

Both the other posters are correct, make sure to read all the instructions, and follow the key and instructions as best you can. If there is a photo of the finished project, that might help you to understand the key better, but it is important to read all of the instructions through. One thing I did want to mention is that occasionally a chart is printed incorrectly, and symbols are used more than once. Once you have read through all the instructions and looked closely at the key, if the symbols really are duplicates, but with different colors, the best thing is to check with the designer/manufacturer. If it is a kit, go to the kit maker (Dimensions, Candamar, Janlynn, etc), if it is a chart by a specific designer, try their website first (if they have one) - many of them post corrections/errata for printings on their sites. Also, there are discussion groups online (here at Yahoo Groups, at Yuku Boards, etc.), many that are focused on specific designers. If you can't get a response from the designer, you can often get help from someone who has already stitched the same pattern you're working on. But at the end of the day, if you can't figure it out, take a minute and look at your materials and make some choices for what to do based on what you want your final project to look like. Don't like blending filament? - skip it, or use a metallic the same color as the base floss instead. Make changes you will be happy about, and apply them consistently to the same symbols and you should still get excellent results. Remember, there are only two rules in needlework: Thread goes through needle, needle goes through fabric - the rest is up to you! Have fun creating your own unique artwork!