Believe it or not, the simplest and probably best solution is to sew the patches on.
I've used different types of fabric glue in the past and all of them were very disappointing. They left ugly spots on the fabric (as if you had spilled sauce on your clothing). None of them held the fabric together after the first wash, but not all of them could be washed out, so the ugly stains remained.
Fusing or fusable interfacing works better to combine 2 pieces of fabric, but fusing always makes the fabric stiffer and takes away any stretch. In some areas you want that effect, like in shirt collars, but in other areas this would look and feel very odd. The advantage is that fusing can be peeled off again. But since it fuses with fabric by melting glue, it might also leave stains.
Sewing patches on clothing for a short while is dead simple. Please don't think you have to stitch as fine and evenly as a machine. We're all humans and no machines, we don't have to be perfect. A stitch length of about 5 mm or 1/4 inch is sufficient to securely sew fabric. If the patch is only supposed to stay on for a short while (like for a costume you only want to wear once), you can go with 1 cm / 3/8 inch stitch length.
You don't even need to tie any knots in the thread. Just start with a really tiny stitch (about 1mm long) and then stitch a second time over the first one. That's enough to secure your thread in the fabric. If you're afraid the end might slip out, stitch a third time over the same stitch. Do the same if you run out of thread and you never need to tie tiny knots in your thread.
If you don't own a sewing machine, but hand sewing is not appealing to you, you might find a friend, family member or neighbor with a sewing machine you can borrow. There are also "makers spaces" where you can use machines and tools for your projects (usually for a monthly payment). A local repair café is another solution, if they have a sewing machine. Some sewing machine shops might lend out machines or let you use it on-site for an hourly fee. And lastly there are different social media portals like facebook groups or local neighborhood networks where you might ask strangers in your local area if they would lend you their sewing machine. It's a great opportunity to get to know new people in these crazy times and they might also give you some advice (like how to sew an elastic seam).
