What does your pattern tell you to do? Do you have the numbers the pattern says you will at that point or is there something that has caused a change? Where is the join falling?
This statement of yours confuses me:
If I decrease the stitches on my needles down to 25 then my thighs will be way too big.
I'm, of course, not picturing what you are doing properly I'm sure, but wouldn't any decreases be making something smaller, not bigger?
Did you work these from the waist down or the leg up? Where did the last knitting you did end, and where are the held stitches?
That is a lot of questions and you may not want to answer them all, but pick the ones that you think would help the most.