Do a full factory reset on the AE.
Setup again and use all short names, no spaces and pure alphanumeric.
If there are wireless issues, IMHO it is better to use different names for 2.4ghz and 5ghz at least until you sort where the issues are.
Use fixed wireless channels.. for 2.4ghz there are only 3 non-overlapping channels 1, 6, 11 (or 13 in ETSI regions). Try each in turn. 5ghz is less of an issue, Try low down,, 36-40 and one of the higher channels.. >150.
Use WPA2 Personal security with password, 10-20 characters enough except for the most paranoid.. pure alphanumeric.
For each laptop clear out all the old networks.. totally empty the retained networks. Then discover the wireless network again and set it up.. that is enough to fix it for most.
See Tesserax doco on issues with sleep .. these can also help with your dropping out.
https://discussions.apple.com/docs/DOC-3411
But you need to be in areas of the house that get at least reasonable signal and not too much interference. If you are in a heavily used wireless area.. check what is available in terms of free channels or force it to 5ghz.
I agree with John.. the latest firmware is not a fix.. indeed people generally report more issues.. 7.6.3 is not great.. stick to 7.6.1 for now.