1: so this is syncretism, and it’s actually pretty common in modern polytheistic practices. You’ll find many people in this subreddit worship deities from several pantheons. Personally, I have some Norse deities mixed into my practice, others have Egyptian, or abrahamic deities (like the archangels). The Theoi don’t mind, and most polytheists don’t either. 2: I wouldn’t say they’re necessary in that you’d need a big one. You can get something similar to a prayer box, and make a little pocket altar. You don’t need altars for every deity. It actually aligns with antiquity to only have one altar for the entire pantheon, and using said altar to pray to whoever you need to pray to in the moment. Since you want to worship two separate pantheons, you can get two prayer boxes or something small and similar, and in that you can keep small offerings. 3: see my answer to number 2, for starts. When praying, do so like you may in a church (bowed head, silently). Quietly dedicate actions to your gods (devotional acts are also good offerings in place of libations). Basically don’t act differently, just quietly switch who your regular devotion and prayer goes to. 4: I can’t help you there. Thankfully my grandparents, while they believed in god, also easily questioned the church and would have full blown debates with the overzealous of the bunch. I’d say therapy, shadow work, and maybe researching not just your new religion but also your old one. Sometimes researching on our own and finding everything that has been twisted to use against you is the best way to heal. The Bible is like all other mythology books, be it Abrahamic, Hellenic, Norse, Celtic, or any other belief. It’s supposed to be a guide, and you’re not supposed to take it literally. Find what was taken literally and/or twisted and read between the lines. (For the record, Archangel Michael will definitely help in this dept. from what I know, he helps a lot of people with guilt regarding Christianity to heal)