Can 'to infinitive as adjective' modify person?

Oh, those are both wrong, wrong, wrong.

First off, with both answers, you're losing the word 'can', which is a necessary part of the original sentence. 'Can' shows ability. Adding an infinitive form of a totally different verb gets rid of 'can' and you lose the sense of the sentence.

Second, you can make #1 right by switching 'to' to 'who'. E. g. I have some friends who play soccer well. In that instance, 'can' is understood. Essentially the sentence means I have some friends who can (or are able to) play soccer well. That is when 'can' is understood, but the infinitive form loses that.

Third, I wish I knew what was up with answer #2. Again, you can swap 'to' for 'who', but then you will also need to swap 'be' for the form of 'to be' which works with third person plural, which is 'are'. E. g. I have some friends who are good at playing soccer.

Your colleague needs to go back to school if s/he thinks either answer is correct English.

thank you for your generous answer.
I also think you're absolutely right. when I first saw my student's answer, I knew #1 and #2 were wrong but I was not sure I could persuade my colleague.
I definitely could use your explanation. thanks
According to your explanation that 'can' is very important in the original sentence and I understood that. but here's what I need to know again.

Question , do you think that #1 or #2 is grammatically flawless?
If not, how can I let them know that they're grammatically wrong?

Neither is flawless, as I stated. Here's a good site for grammar: http://www.quickanddirtytips.com/grammar-girl