I split the frequencies as suggested and that's helped a bit.
However the wifi is still off and on around the house and has very slow speeds a few feet away from the router (compared to how it before Christmas - it was terrific for years but now close to unusable!).
For example, when I'm downstairs (the router is on the 1st floor) and open up my laptop it doesn't connect even though things were running perfectly on the 1st floor.
What else could be wrong?