Using a guilded alter in your home for prayer will not give double XP.
Ectofungus is also not doubled.
Burying bones regularly is doubled.
If you have access to Prif, most people train prayer cleansing crystals in Hefin, coz that is also doubled, making it afk & cost effective.
If you click NEWS at the top of this page it takes you to the news page.
I recommend you check this page daily or every few days.
There you will see different Jagex news posts, one of which mentions dxp w/e.
In that article at the very starts is a link which takes you to the following page:
https://www.runescape.com/community/double-xp-weekend
There you will find details of what is & is not included.
You won't be able to get double xp on poh alters, but you still have time to plan something else you'd rather do.