Well,as someone who has gone about practicing magick as a whole in the broom closet,I can take a shot at answering this.
First,I will point you,to EA Koetting’s video on it:
which while not a 100% helpful in answering your question,is indeed going to lay out the fundamental thought,that not having a permanent altar,and not being allowed to practice your magick will not harm it.And in fact,it may even act as a strong catalyst.
With that in mind,first,you aren’t in such a strong need of implements.Yes,they come in handy,but try to make them blend into your mundane circumstance.
EA says in Evoking Eternity,that you can consecrate your ritual items each evocation.While surely the intent of this is to have them grow stronger and stronger,I always consecrate them,and then just desecrate them,by commanding them after evocation to be come mortal items once more.
The chalice I use,albeit rarely,is an antique my grandfather gave me,which is why it sits in small cupboards,never to be used.The athame I use,is a kitchen knife that happens to be double-edged,and have a black handle and be perfect.I use it both for cooking,and for ritual work,with no ill effect,so long as I don’t cook with it while it’s consecrated,or do magick with it while it’s not.The circle I use,is not really a circle.I use the design of the Circle of Solomon,or the Universal Circle,but I draw it on the floor in chalk.After repeating this a couple of time,the light shines on the spot in a specific manner that I can always see the circle,effectively eliminating my need to draw one each time I do ritual.Interestingly,no muggle is capable of perceiving it,and this is something I’ve been assured by the demons I work with.No muggle can see it.
If you have time to perform magick,while your father and brother are away,do so at that time.And be sure to put everything away when you’re done.
If you’re gonna open sigils,you may wanna draw them on toilet paper.It has worked fine for me,and I can throw them away more easily and make it look less odd(I cringe if I throw real paper in the toilet)
Which reminds me,exploit your toilet as a cauldron(that’s not something I ever thought I’d say XD) which is to say,throw burned sigils,scatter ashes,and use it to carry your spell,through the gateways of water.
If you’re not capable of using candle magic,or burning sigils,because it’s the fire part that bothers you,use water instead.Water,is another perfectly natural gateway into the other realms,and if you can scry into water,you can also send messages and do candle magic,with water.That’s a little trick Paimon told me of.
Pouring water over sigils also apparently closes them if you command the sigil to close.Perform spells at night,and try to hide any notes,into tiny knooks and crannies,if you even need to keep notes.
For scrying mirrors,take a piece of black cardboard and place it on the inside of a picture frame.The cardboard came with the mirror,and I love my current scrying mirror,and it’s completely normal to have an empty picture frame.
Do not focus so much on burning incense,develop your senses.Try not to slaughter animals,blood sacrifice is an amazing catalyst that you can use when you will.
This may not be the best advice,and many black magicians will disagree,but you can try immersing yourself in the Christian saint.Not only will it remove suspicion off of them,so they won’t actively be looking for black magic related items,but it will also give you just another system to exploit to get what you want.Praying with enough fervor,whether to Allah,Jehovah,Krishna,or Satan,will yield results,and it does not matter whom one is praying to,nor why,but how.
You can also ask some entity to help you disguise your workings.That may help.Or develop your senses to such a degree that the spirits may inform you when someone is walking towards the room where you’re operating so you can put it all away.
Just some suggestions,will come back later.