十来个 and 十多个 means in the neighborhood of 10 but, it is more than 10, it can not be less than 10. You can not seperated them because these three words have to be together to means one thing. 十来个 is more colloquial, mostly used by the people in the northern part of China, 十多个 is most common, it is being used every where. Both 十来个 and 十多个 means the same. Addition: 来 here, it is refering the number that is comming close to, it is possible that 十来个 meaning close to 10. However, 十来个 is colloquial, the concept of these words by most of the Chinese speakers are considered in the neiborhood of 10, they are not sure the exact number. "多" means more. We can not justify the colloquial language what is written. For example, in English, "why" and "how come", they both means the same but they were written differently. Where most people use 十多个 ( more than 10) to means around 10. Some people, perhaps they are scholars try to make themselves different, so they change to 十来个 (close to 10). Anyway, Chinese languages and culture are carried over from the past, we just accept it as is condition. However, there are still some scholars trying to differentiate themselves, making the chinese into an argument. What the normal people will react in the same sistuation? I believe most chinese will considered 十来个 and 十多个 meaning in the neighborhood of 10.

“十来个”表示十个左右，“十多个”表示多于十个

十来个: less or more than 10 十多个: more than 10

十来个 means the numbers maybe more than ten maybe less , it 's not sure . but 十多个 means the numbers must more than ten , and less than twety .

"十来个/十多个"both mean more than 10. one is oral and imformal, another is formal . But strickly speaking, "十来个 "only used in Beijing and the northern people who speak Beijing dialect( not stardard Mandarin) . When northern people use "十来个", some of them mean more than 10（11-14） or less than 10（7-9）. But when we heard '十来个", we mean more than 10 ,less than 20. And we usually don't use "十来个"for you would not hear it in standard mandarin and it sounds a little rustic. "十多个" and" 十几个" are more often used in the south and even nationwide.. one is oral and another is both in oral and written. Fuzziness of language is a typical factor in Chinese.