I don't think these two teams can give Real Madrid or Barcelona a hard time. Real Madrid and Barcelona will win these matches without any problems. Also, since the situation is at a critical level in the league, I think Real Madrid will play the matches more focused and win most of their matches. The Arsenal defeat may have been a shake-up match for them. Perhaps such a defeat was necessary on the way to becoming a strong Real Madrid again.
Leganes and Alaves are the teams at the bottom of the standings, they should not trouble Barcelona and Madrid. This week should be 3 points for them. Atletico will also face a weak team Valladolid, it should not be a threat to them and the standings will not change for this week. Barcelona will still be at the top, followed by Madrid and Atletico.
It is true, sometimes during some weeks big teams face small teams and the result is given before the game even starts. We are going to see Barcelona and Real Madrid win this week, so it is not going to be a great period for lower teams.
Plus, betting on these two teams to win, even as a parlay, isn't going to make that much money to anyone, so it is not going to be a big deal at all. I am pretty sure we are going to have a hard time doing this, but that doesn't mean we are going to make too much money from them neither. What we need to do here is add another one, like maybe add atletico Madrid or bilbao, if you do that then bet could get bigger and maybe then you could be making some good return but even then not so much.