My answer will mostly be my own interpretations.
To me and many others veganism entails cutting out harm to others where it is not necessary. I don't eat animal products because I can get the same nutrients elsewhere. The pleasure that food gives me, I found in other foods. I didn't have to give up much (or in many cases anything) that makes my life what it is and what I do and enjoy in it. If I can have what is necessary to maintain my lifestyle with alternatives and slight inconvenience but not major (such as getting cosmetic products from a different store or cooking more often, but not moving from the city at expense of my financial stability), I will take the alternatives and slight inconveniences.
Vaccines are not wrong to me. To live my life fully I have to avoid illness where I can. Many benefits the medical field has provided me with entail harm to animals. Veganism is about reducing suffering wherever possible, right? But what does this mean? Possible to survive in the present, or possible to live a normal life in modern society. To me it means that where the benefits of harm do not outweigh the actual harm, the action is wrong. My primary responsibility is myself. I prioritise my own health. For this, I will need medical practices. If there was cruelty involved in creating a better sunscreen or something cosmetic, I would take the second best (cruelty free) sunscreen and dismiss the importance of cosmetics.
Pets is a VERY grey area to me, mostly because I will be biased. I love my cats. They do not fit the vegan lifestyle. I got them before I went vegan but I am attached to them and their wellbeing is important to me only because of personal contact with them. Having a carnivorous pet is probably not very vegan of me. It is definitely contributing to harm. But I am not perfect. I try not to contribute to cruelty as much as I can, but I'm personally just not willing to do that at the expense of the people and animals close to me that I love. Having a pet is mostly for one's own comfort and company (sometimes entertainment) so it's quite selfish and not pro vegan. I can still contribute significantly less by being vegan in as many other areas of life as I can uphold.
To the humane killing topic I can't contribute much as I don't know a lot about it. Killing a predator to save its prey is just invasive to nature and humans already got their hands in on way too many natural occurences. Killing a predator that isn't hunting where it naturally would, seems to be about restoring nature. This I cannot oppose. I can however oppose it if there are more ethical alternatives such as relocation, which I'm sure there probably will be.
Children... Having kids on a vegan diet isn't unhealthy as far as I know. If this child chooses to eat meat later in life, that's up to the child. If a child grows up to be a mass murderer (of humans), it surely wasn't the parents' intention. They could not be held accountable. It is a parent's responsibility to teach the child to be as good of a person as he/she can be. A parent transfers his/her own moral guidelines to the child in order to achieve this. As the child grows up, the child will challenge this or follow it or oppose it. There is a point where a parent loses control over the decisions the child makes. Adopting is the best choice because it's best for our own species, even if disregarding a bigger societal issue of overpopulation. I won't criticise anyone who doesn't adopt because there's more at play than convenience or temporary pleasure like with eating animal products. But if you want kids, consider adoption please.
You mentioned evolutionary drive, which is interesting to me. I don't have the evolutionary drive to hunt. Most meat is just conveniently bought wrapped in plastic. We lost this somewhere in our development as species. Hunting as a hobby is the same as all other passion filled hobbies, and I've never heard of someone NEEDING to scrapbook or do yoga or paint miniature figures or else they'll die. But it is just something that they very much enjoy. I'll give up sewing if it came at great expense to others. We do, however, have a drive to reproduce.
Buying vegan alternatives from a company that also has unethical products would influence the supply and demand reaction. You create a demand and they'll supply more of the vegan alternative. Lessen the demand for animal products and supply will drop. Some companies might turn to advertising more aggressively at first, to get something for the current stock they have. But when this doesn't work because the cheese commercial didn't make you buy cheese, then they'll have to make less cheese or they will lose a lot of money. If I had to stop supporting companies who have done something wrong then I would have to move away from society completely. A better approach is to influence the way they operate, they will always shift to where there is financial gain. Your choices aren't as limited as we often think. The only change I had to make was cooking more often. If there is lab grown meat and a hobby farm competing, it wouldn't matter to me. I don't eat meat. If lab grown meat had a small footprint then I would buy it. If it had a a large impact, I'll just stay plant based.
Where to draw the line? Try to reduce cruelty wherever you can. If you have absolutely nothing to eat but meat, then what can you do? Your survival is important. But I've never heard of someone in this situation. What do you lose when you replace animal products with a plant based diet? Not much. What do you lose when you refuse antivenom after a snakebite? Your life. Do what is possible to help the world around you and cut out what is not necessary.
In conclusion, do what you can and don't do what you don't have to. And also, nobody is perfect. There is no perfect vegan. But at least try.