B2 Visa only for Brother-in-law.. Sister already has Visa

[aronish]

Hi,

I'm facing a little tricky situation here. Quick help would be appreciated.
My sister already has a valid B2 stamp which she got before she got married. I was not the sponsor but my Uncle who is a citizen here sponsored her. I'm sponsoring my brother-in-law for B2 visitor and both of them would be travelling here and I will be taking care of all the expenses. As per the instructions, I have prepared the Invitation letter only for him. Also in I-134 document, I mentioned that he is married but did not mention my sister details in Spouse column as she is not applying for Visa.

1. Now the question is that his DS-160 has a column called Travel companion. Should he say Yes or No ?
2. If he says Yes, since I will be taking up the expense for both, do I need to incude my sister in Invitation letter and also mention her name in my brother-in-law's I-134 document ?
Because if the interviewer asks who will be taking my sister's expense and he gives my name, would there be a problem if I don't list her on the invitation letter ?

Please help.

[immihelp]

1. Yes.
2. Include both of them in the invitation letter.