Gurkha's,

there will be many Nepalese people travelling that route and this time of the month, many more because of the summer break (a lot of students and a lot of families due to summer break of their kids), so, I do not really think that there is going to be a problem. You may even find some companion from your city straight till KTM. From, Frankfurt or London, wherever the transit may be, more and more Nepalese will be flying that route as this route is one of the simplest, easiest, and popular route to get to KTM. In Qatar, you can't imagine how many Nepalese you would find-believe me, it will be like your in-laws have already reached Nepal!

So, don't worry too much. But as a precaution, keep looking for confirmed people travelling on that day and that route or arrange cards like Raman has suggested. BTW, what city are they flying from. Good Luck!